diff --git a/src/Client.php b/src/Client.php
index e54cb3d29..84e00baf7 100644
--- a/src/Client.php
+++ b/src/Client.php
@@ -178,7 +178,10 @@ public function captureException(\Throwable $exception, ?Scope $scope = null, ?E
      */
     public function captureEvent(Event $event, ?EventHint $hint = null, ?Scope $scope = null): ?EventId
     {
-        $event = $this->prepareEvent($event, $hint, $scope);
+        // Client reports don't need to be augmented in the prepareEvent pipeline.
+        if ($event->getType() !== EventType::clientReport()) {
+            $event = $this->prepareEvent($event, $hint, $scope);
+        }
 
         if ($event === null) {
             return null;
diff --git a/src/ClientReport/ClientReport.php b/src/ClientReport/ClientReport.php
new file mode 100644
index 000000000..0b580574e
--- /dev/null
+++ b/src/ClientReport/ClientReport.php
@@ -0,0 +1,45 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Sentry\ClientReport;
+
+class ClientReport
+{
+    /**
+     * @var string
+     */
+    private $reason;
+
+    /**
+     * @var string
+     */
+    private $category;
+
+    /**
+     * @var int
+     */
+    private $quantity;
+
+    public function __construct(string $category, string $reason, int $quantity)
+    {
+        $this->category = $category;
+        $this->reason = $reason;
+        $this->quantity = $quantity;
+    }
+
+    public function getCategory(): string
+    {
+        return $this->category;
+    }
+
+    public function getQuantity(): int
+    {
+        return $this->quantity;
+    }
+
+    public function getReason(): string
+    {
+        return $this->reason;
+    }
+}
diff --git a/src/ClientReport/ClientReportAggregator.php b/src/ClientReport/ClientReportAggregator.php
new file mode 100644
index 000000000..96b8e07da
--- /dev/null
+++ b/src/ClientReport/ClientReportAggregator.php
@@ -0,0 +1,79 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Sentry\ClientReport;
+
+use Sentry\Event;
+use Sentry\State\HubAdapter;
+use Sentry\Transport\DataCategory;
+
+class ClientReportAggregator
+{
+    /**
+     * @var self
+     */
+    private static $instance;
+
+    /**
+     * Nested array for local aggregation. The first key is the category and the second one is the reason.
+     *
+     * ```
+     * [
+     *  'example-category' => [
+     *      'example-reason' => 10
+     *   ]
+     * ]
+     *```
+     *
+     * @var array<array<string, int>>
+     */
+    private $reports = [];
+
+    public function add(DataCategory $category, Reason $reason, int $quantity): void
+    {
+        $category = $category->getValue();
+        $reason = $reason->getValue();
+        if ($quantity <= 0) {
+            $client = HubAdapter::getInstance()->getClient();
+            if ($client !== null) {
+                $logger = $client->getOptions()->getLoggerOrNullLogger();
+                $logger->debug('Dropping Client report with category={category} and reason={} because quantity is zero or negative ({quantity})', [
+                    'category' => $category,
+                    'reason' => $reason,
+                    'quantity' => $quantity,
+                ]);
+
+                return;
+            }
+        }
+        $this->reports[$category][$reason] = ($this->reports[$category][$reason] ?? 0) + $quantity;
+    }
+
+    public function flush(): void
+    {
+        if (empty($this->reports)) {
+            return;
+        }
+        $reports = [];
+        foreach ($this->reports as $category => $reasons) {
+            foreach ($reasons as $reason => $quantity) {
+                $reports[] = new ClientReport($category, $reason, $quantity);
+            }
+        }
+        $event = Event::createClientReport();
+        $event->setClientReports($reports);
+
+        HubAdapter::getInstance()->captureEvent($event);
+        $this->reports = [];
+    }
+
+    public static function getInstance(): self
+    {
+        if (self::$instance === null) {
+            self::$instance = new self();
+        }
+
+        return self::$instance;
+    }
+}
diff --git a/src/ClientReport/Reason.php b/src/ClientReport/Reason.php
new file mode 100644
index 000000000..3c66bf7d4
--- /dev/null
+++ b/src/ClientReport/Reason.php
@@ -0,0 +1,102 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Sentry\ClientReport;
+
+class Reason
+{
+    /**
+     * @var string
+     */
+    private $value;
+
+    /**
+     * @var array<self>
+     */
+    private static $instances = [];
+
+    public function __construct(string $value)
+    {
+        $this->value = $value;
+    }
+
+    public static function queueOverflow(): self
+    {
+        return self::getInstance('queue_overflow');
+    }
+
+    public static function cacheOverflow(): self
+    {
+        return self::getInstance('cache_overflow');
+    }
+
+    public static function bufferOverflow(): self
+    {
+        return self::getInstance('buffer_overflow');
+    }
+
+    public static function ratelimitBackoff(): self
+    {
+        return self::getInstance('ratelimit_backoff');
+    }
+
+    public static function networkError(): self
+    {
+        return self::getInstance('network_error');
+    }
+
+    public static function sampleRate(): self
+    {
+        return self::getInstance('sample_rate');
+    }
+
+    public static function beforeSend(): self
+    {
+        return self::getInstance('before_send');
+    }
+
+    public static function eventProcessor(): self
+    {
+        return self::getInstance('event_processor');
+    }
+
+    public static function sendError(): self
+    {
+        return self::getInstance('send_error');
+    }
+
+    public static function internalSdkError(): self
+    {
+        return self::getInstance('internal_sdk_error');
+    }
+
+    public static function insufficientData(): self
+    {
+        return self::getInstance('insufficient_data');
+    }
+
+    public static function backpressure(): self
+    {
+        return self::getInstance('backpressure');
+    }
+
+    public function getValue(): string
+    {
+        return $this->value;
+    }
+
+    public function __toString()
+    {
+        return $this->value;
+    }
+
+    private static function getInstance(string $value): self
+    {
+        if (!isset(self::$instances[$value])) {
+            self::$instances[$value] = new self($value);
+        }
+
+        return self::$instances[$value];
+    }
+}
diff --git a/src/Event.php b/src/Event.php
index e2d2a8c0f..334c34b6a 100644
--- a/src/Event.php
+++ b/src/Event.php
@@ -4,6 +4,7 @@
 
 namespace Sentry;
 
+use Sentry\ClientReport\ClientReport;
 use Sentry\Context\OsContext;
 use Sentry\Context\RuntimeContext;
 use Sentry\Logs\Log;
@@ -210,6 +211,11 @@ final class Event
      */
     private $profile;
 
+    /**
+     * @var ClientReport[]
+     */
+    private $clientReports;
+
     private function __construct(?EventId $eventId, EventType $eventType)
     {
         $this->id = $eventId ?? EventId::generate();
@@ -252,6 +258,11 @@ public static function createMetrics(?EventId $eventId = null): self
         return new self($eventId, EventType::metrics());
     }
 
+    public static function createClientReport(?EventId $eventId = null): self
+    {
+        return new self($eventId, EventType::clientReport());
+    }
+
     /**
      * Gets the ID of this event.
      */
@@ -978,4 +989,22 @@ public function getTraceId(): ?string
 
         return null;
     }
+
+    /**
+     * @param ClientReport[] $clientReports
+     */
+    public function setClientReports(array $clientReports): self
+    {
+        $this->clientReports = $clientReports;
+
+        return $this;
+    }
+
+    /**
+     * @return ClientReport[]
+     */
+    public function getClientReports(): array
+    {
+        return $this->clientReports;
+    }
 }
diff --git a/src/EventType.php b/src/EventType.php
index 679f96633..5c068d0f1 100644
--- a/src/EventType.php
+++ b/src/EventType.php
@@ -52,6 +52,11 @@ public static function metrics(): self
         return self::getInstance('trace_metric');
     }
 
+    public static function clientReport(): self
+    {
+        return self::getInstance('client_report');
+    }
+
     /**
      * List of all cases on the enum.
      *
@@ -65,6 +70,7 @@ public static function cases(): array
             self::checkIn(),
             self::logs(),
             self::metrics(),
+            self::clientReport(),
         ];
     }
 
diff --git a/src/Logs/LogsAggregator.php b/src/Logs/LogsAggregator.php
index e2fb5ea78..92bff3e47 100644
--- a/src/Logs/LogsAggregator.php
+++ b/src/Logs/LogsAggregator.php
@@ -6,11 +6,14 @@
 
 use Sentry\Attributes\Attribute;
 use Sentry\Client;
+use Sentry\ClientReport\ClientReportAggregator;
+use Sentry\ClientReport\Reason;
 use Sentry\Event;
 use Sentry\EventId;
 use Sentry\SentrySdk;
 use Sentry\State\HubInterface;
 use Sentry\State\Scope;
+use Sentry\Transport\DataCategory;
 use Sentry\Util\Arr;
 use Sentry\Util\Str;
 
@@ -35,6 +38,11 @@ public function add(
         array $values = [],
         array $attributes = []
     ): void {
+        if (\count($this->logs) > 5) {
+            ClientReportAggregator::getInstance()->add(DataCategory::logBytes(), Reason::bufferOverflow(), 1);
+
+            return;
+        }
         $timestamp = microtime(true);
 
         $hub = SentrySdk::getCurrentHub();
diff --git a/src/Serializer/EnvelopItems/ClientReportItem.php b/src/Serializer/EnvelopItems/ClientReportItem.php
new file mode 100644
index 000000000..5d87b1b70
--- /dev/null
+++ b/src/Serializer/EnvelopItems/ClientReportItem.php
@@ -0,0 +1,30 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Sentry\Serializer\EnvelopItems;
+
+use Sentry\ClientReport\ClientReport;
+use Sentry\Event;
+
+class ClientReportItem implements EnvelopeItemInterface
+{
+    public static function toEnvelopeItem(Event $event): ?string
+    {
+        $reports = $event->getClientReports();
+
+        $headers = ['type' => 'client_report'];
+        $body = [
+            'timestamp' => $event->getTimestamp(),
+            'discarded_events' => array_map(function (ClientReport $report) {
+                return [
+                    'category' => $report->getCategory(),
+                    'reason' => $report->getReason(),
+                    'quantity' => $report->getQuantity(),
+                ];
+            }, $reports),
+        ];
+
+        return \sprintf("%s\n%s", json_encode($headers), json_encode($body));
+    }
+}
diff --git a/src/Serializer/PayloadSerializer.php b/src/Serializer/PayloadSerializer.php
index 45de0f29f..3204f5900 100644
--- a/src/Serializer/PayloadSerializer.php
+++ b/src/Serializer/PayloadSerializer.php
@@ -8,6 +8,7 @@
 use Sentry\EventType;
 use Sentry\Options;
 use Sentry\Serializer\EnvelopItems\CheckInItem;
+use Sentry\Serializer\EnvelopItems\ClientReportItem;
 use Sentry\Serializer\EnvelopItems\EventItem;
 use Sentry\Serializer\EnvelopItems\LogsItem;
 use Sentry\Serializer\EnvelopItems\MetricsItem;
@@ -39,23 +40,26 @@ public function __construct(Options $options)
      */
     public function serialize(Event $event): string
     {
-        // @see https://develop.sentry.dev/sdk/envelopes/#envelope-headers
-        $envelopeHeader = [
-            'sent_at' => gmdate('Y-m-d\TH:i:s\Z'),
-            'dsn' => (string) $this->options->getDsn(),
-            'sdk' => $event->getSdkPayload(),
-        ];
+        $envelopeHeader = null;
+        if ($event->getType() !== EventType::clientReport()) {
+            // @see https://develop.sentry.dev/sdk/envelopes/#envelope-headers
+            $envelopeHeader = [
+                'sent_at' => gmdate('Y-m-d\TH:i:s\Z'),
+                'dsn' => (string) $this->options->getDsn(),
+                'sdk' => $event->getSdkPayload(),
+            ];
 
-        if ($event->getType()->requiresEventId()) {
-            $envelopeHeader['event_id'] = (string) $event->getId();
-        }
+            if ($event->getType()->requiresEventId()) {
+                $envelopeHeader['event_id'] = (string) $event->getId();
+            }
 
-        $dynamicSamplingContext = $event->getSdkMetadata('dynamic_sampling_context');
-        if ($dynamicSamplingContext instanceof DynamicSamplingContext) {
-            $entries = $dynamicSamplingContext->getEntries();
+            $dynamicSamplingContext = $event->getSdkMetadata('dynamic_sampling_context');
+            if ($dynamicSamplingContext instanceof DynamicSamplingContext) {
+                $entries = $dynamicSamplingContext->getEntries();
 
-            if (!empty($entries)) {
-                $envelopeHeader['trace'] = $entries;
+                if (!empty($entries)) {
+                    $envelopeHeader['trace'] = $entries;
+                }
             }
         }
 
@@ -80,6 +84,13 @@ public function serialize(Event $event): string
             case EventType::metrics():
                 $items[] = MetricsItem::toEnvelopeItem($event);
                 break;
+            case EventType::clientReport():
+                $items[] = ClientReportItem::toEnvelopeItem($event);
+                break;
+        }
+
+        if ($envelopeHeader === null) {
+            return \sprintf("{}\n%s", implode("\n", array_filter($items)));
         }
 
         return \sprintf("%s\n%s", JSON::encode($envelopeHeader), implode("\n", array_filter($items)));
diff --git a/src/Transport/DataCategory.php b/src/Transport/DataCategory.php
new file mode 100644
index 000000000..907404f7d
--- /dev/null
+++ b/src/Transport/DataCategory.php
@@ -0,0 +1,83 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Sentry\Transport;
+
+class DataCategory
+{
+    /**
+     * @var string
+     */
+    private $value;
+
+    /**
+     * @var array<self>
+     */
+    private static $instances = [];
+
+    public function __construct(string $value)
+    {
+        $this->value = $value;
+    }
+
+    public static function error(): self
+    {
+        return self::getInstance('error');
+    }
+
+    public static function transaction(): self
+    {
+        return self::getInstance('transaction');
+    }
+
+    // TODO: not sure if this should be called monitor or checkIn.
+    public static function checkIn(): self
+    {
+        return self::getInstance('monitor');
+    }
+
+    public static function logItem(): self
+    {
+        return self::getInstance('log_item');
+    }
+
+    public static function logBytes(): self
+    {
+        return self::getInstance('log_bytes');
+    }
+
+    public static function profile(): self
+    {
+        return self::getInstance('profile');
+    }
+
+    public static function metric(): self
+    {
+        return self::getInstance('trace_metric');
+    }
+
+    public static function internal(): self
+    {
+        return self::getInstance('internal');
+    }
+
+    public function getValue(): string
+    {
+        return $this->value;
+    }
+
+    public function __toString()
+    {
+        return $this->value;
+    }
+
+    private static function getInstance(string $value): self
+    {
+        if (!isset(self::$instances[$value])) {
+            self::$instances[$value] = new self($value);
+        }
+
+        return self::$instances[$value];
+    }
+}
diff --git a/tests/ClientReport/ClientReportAggregatorTest.php b/tests/ClientReport/ClientReportAggregatorTest.php
new file mode 100644
index 000000000..9746d9bf5
--- /dev/null
+++ b/tests/ClientReport/ClientReportAggregatorTest.php
@@ -0,0 +1,87 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Sentry\Tests\ClientReport;
+
+use PHPUnit\Framework\TestCase;
+use Sentry\Client;
+use Sentry\ClientReport\ClientReportAggregator;
+use Sentry\ClientReport\Reason;
+use Sentry\Options;
+use Sentry\SentrySdk;
+use Sentry\Tests\StubLogger;
+use Sentry\Tests\StubTransport;
+use Sentry\Transport\DataCategory;
+
+class ClientReportAggregatorTest extends TestCase
+{
+    protected function setUp(): void
+    {
+        ini_set('zend.exception_ignore_args', '0');
+        StubTransport::$events = [];
+        StubLogger::$logs = [];
+        SentrySdk::init()->bindClient(new Client(new Options([
+            'logger' => StubLogger::getInstance(),
+        ]), StubTransport::getInstance()));
+    }
+
+    public function testAddClientReport(): void
+    {
+        ClientReportAggregator::getInstance()->add(DataCategory::profile(), Reason::eventProcessor(), 10);
+        ClientReportAggregator::getInstance()->add(DataCategory::error(), Reason::beforeSend(), 10);
+        ClientReportAggregator::getInstance()->flush();
+
+        $this->assertCount(1, StubTransport::$events);
+        $reports = StubTransport::$events[0]->getClientReports();
+        $this->assertCount(2, $reports);
+
+        $report = $reports[0];
+        $this->assertSame(DataCategory::profile()->getValue(), $report->getCategory());
+        $this->assertSame(Reason::eventProcessor()->getValue(), $report->getReason());
+        $this->assertSame(10, $report->getQuantity());
+
+        $report = $reports[1];
+        $this->assertSame(DataCategory::error()->getValue(), $report->getCategory());
+        $this->assertSame(Reason::beforeSend()->getValue(), $report->getReason());
+        $this->assertSame(10, $report->getQuantity());
+    }
+
+    public function testClientReportAggregation(): void
+    {
+        ClientReportAggregator::getInstance()->add(DataCategory::profile(), Reason::eventProcessor(), 10);
+        ClientReportAggregator::getInstance()->add(DataCategory::profile(), Reason::eventProcessor(), 10);
+        ClientReportAggregator::getInstance()->add(DataCategory::profile(), Reason::eventProcessor(), 10);
+        ClientReportAggregator::getInstance()->add(DataCategory::profile(), Reason::eventProcessor(), 10);
+        ClientReportAggregator::getInstance()->flush();
+
+        $this->assertCount(1, StubTransport::$events);
+        $reports = StubTransport::$events[0]->getClientReports();
+        $this->assertCount(1, $reports);
+
+        $report = $reports[0];
+        $this->assertSame(DataCategory::profile()->getValue(), $report->getCategory());
+        $this->assertSame(Reason::eventProcessor()->getValue(), $report->getReason());
+        $this->assertSame(40, $report->getQuantity());
+    }
+
+    public function testNegativeQuantityDiscarded(): void
+    {
+        ClientReportAggregator::getInstance()->add(DataCategory::profile(), Reason::eventProcessor(), -10);
+        ClientReportAggregator::getInstance()->flush();
+
+        $this->assertEmpty(StubTransport::$events);
+        $this->assertNotEmpty(StubLogger::$logs);
+        $this->assertSame(['level' => 'debug', 'message' => 'Dropping Client report with category={category} and reason={} because quantity is zero or negative ({quantity})', 'context' => ['category' => 'profile', 'reason' => 'event_processor', 'quantity' => -10]], StubLogger::$logs[0]);
+    }
+
+    public function testZeroQuantityDiscarded(): void
+    {
+        ClientReportAggregator::getInstance()->add(DataCategory::profile(), Reason::eventProcessor(), 0);
+        ClientReportAggregator::getInstance()->flush();
+
+        $this->assertEmpty(StubTransport::$events);
+        $this->assertCount(1, StubLogger::$logs);
+        $this->assertSame(['level' => 'debug', 'message' => 'Dropping Client report with category={category} and reason={} because quantity is zero or negative ({quantity})', 'context' => ['category' => 'profile', 'reason' => 'event_processor', 'quantity' => 0]], StubLogger::$logs[0]);
+    }
+}
diff --git a/tests/Serializer/PayloadSerializerTest.php b/tests/Serializer/PayloadSerializerTest.php
index 53f3235e8..f3a8c869d 100644
--- a/tests/Serializer/PayloadSerializerTest.php
+++ b/tests/Serializer/PayloadSerializerTest.php
@@ -9,6 +9,7 @@
 use Sentry\CheckIn;
 use Sentry\CheckInStatus;
 use Sentry\Client;
+use Sentry\ClientReport\ClientReport;
 use Sentry\Context\OsContext;
 use Sentry\Context\RuntimeContext;
 use Sentry\Event;
@@ -472,5 +473,21 @@ public static function serializeAsEnvelopeDataProvider(): iterable
 {"items":[{"timestamp":1597790835,"trace_id":"21160e9b836d479f81611368b2aa3d2c","span_id":"d051f34163cd45fb","name":"test-distribution","value":5,"unit":"day","type":"distribution","attributes":{"foo":{"type":"string","value":"bar"}}}]}
 TEXT
         ];
+
+        $event = Event::createClientReport();
+        $event->setClientReports([
+            new ClientReport('error', 'before_send', 10),
+            new ClientReport('profile', 'internal_sdk_error', 50),
+        ]);
+
+        yield [
+            $event,
+            <<<TEXT
+{}
+{"type":"client_report"}
+{"timestamp":1597790835,"discarded_events":[{"category":"error","reason":"before_send","quantity":10},{"category":"profile","reason":"internal_sdk_error","quantity":50}]}
+TEXT
+            ,
+        ];
     }
 }
diff --git a/tests/StubLogger.php b/tests/StubLogger.php
new file mode 100644
index 000000000..571cf2808
--- /dev/null
+++ b/tests/StubLogger.php
@@ -0,0 +1,38 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Sentry\Tests;
+
+use Psr\Log\AbstractLogger;
+
+class StubLogger extends AbstractLogger
+{
+    public static $logs = [];
+
+    /**
+     * @var self
+     */
+    private static $instance;
+
+    public static function getInstance(): self
+    {
+        if (self::$instance === null) {
+            self::$instance = new StubLogger();
+        }
+
+        return self::$instance;
+    }
+
+    /**
+     * @param string $message
+     */
+    public function log($level, $message, array $context = []): void
+    {
+        self::$logs[] = [
+            'level' => $level,
+            'message' => $message,
+            'context' => $context,
+        ];
+    }
+}