diff --git a/src/LaunchDarkly/Impl/Integrations/CurlEventPublisher.php b/src/LaunchDarkly/Impl/Integrations/CurlEventPublisher.php
index 75f95149..7474006f 100644
--- a/src/LaunchDarkly/Impl/Integrations/CurlEventPublisher.php
+++ b/src/LaunchDarkly/Impl/Integrations/CurlEventPublisher.php
@@ -24,6 +24,7 @@ class CurlEventPublisher implements EventPublisher
     private int $_connectTimeout;
     private int $_timeout;
     private bool $_isWindows;
+    private ?string $_httpProxy;
 
     /**
      * The directory named by the payload_temp_dir option, or null if the option is not set.
@@ -59,6 +60,7 @@ public function __construct(string $sdkKey, array $options = [])
         $this->_connectTimeout = intval($options['connect_timeout']);
         $this->_timeout = intval($options['timeout']);
         $this->_isWindows = PHP_OS_FAMILY == 'Windows';
+        $this->_httpProxy = Util::httpProxy($options);
         $this->_payloadTempDir = $this->resolvePayloadTempDir($options['payload_temp_dir'] ?? null);
     }
 
@@ -138,6 +140,9 @@ private function makeCurlRequest(string $payload, ?string $payloadFile = null):
         $args = " -X POST";
         $args.= " --connect-timeout " . $this->_connectTimeout;
         $args.= " --max-time " . $this->_timeout;
+        if ($this->_httpProxy !== null) {
+            $args.= " --proxy " . escapeshellarg($this->_httpProxy);
+        }
 
         foreach ($this->_eventHeaders as $key => $value) {
             $args.= " -H " . escapeshellarg("$key: $value");
@@ -178,13 +183,18 @@ private function makePowershellRequest(string $payloadFile): bool
         }
 
         $scheme = $this->_ssl ? "https://" : "http://";
+        $escapedFile = str_replace("'", "''", $payloadFile);
+        $escapedUri = str_replace("'", "''", $scheme . $this->_host . ":" . $this->_port . $this->_path . "/bulk");
         $args = " Invoke-WebRequest";
         $args.= " -Method POST";
         $args.= " -UseBasicParsing";
-        $args.= " -InFile '$payloadFile'";
+        $args.= " -InFile '$escapedFile'";
         $args.= " -H @{" . $headerString . "}";
-        $args.= " -Uri " . escapeshellarg($scheme . $this->_host . ":" . $this->_port . $this->_path . "/bulk");
-        $args.= " ; Remove-Item '$payloadFile'";
+        if ($this->_httpProxy !== null) {
+            $args.= " -Proxy '" . str_replace("'", "''", $this->_httpProxy) . "'";
+        }
+        $args.= " -Uri '$escapedUri'";
+        $args.= " ; Remove-Item '$escapedFile'";
 
         $cmd = base64_encode(iconv('ISO-8859-1', 'UTF-16LE', $args));
         shell_exec("start /B powershell.exe -encodedCommand $cmd > nul 2>&1");
diff --git a/src/LaunchDarkly/Impl/Integrations/GuzzleEventPublisher.php b/src/LaunchDarkly/Impl/Integrations/GuzzleEventPublisher.php
index fb07b581..ee0283b8 100644
--- a/src/LaunchDarkly/Impl/Integrations/GuzzleEventPublisher.php
+++ b/src/LaunchDarkly/Impl/Integrations/GuzzleEventPublisher.php
@@ -38,6 +38,10 @@ public function __construct(string $sdkKey, array $options = [])
             'timeout' => $options['timeout'],
             'connect_timeout' => $options['connect_timeout']
         ];
+        $proxy = Util::httpProxy($options);
+        if ($proxy !== null) {
+            $this->_requestOptions['proxy'] = $proxy;
+        }
     }
 
     public function publish(string $payload): bool
diff --git a/src/LaunchDarkly/Impl/Integrations/GuzzleFeatureRequester.php b/src/LaunchDarkly/Impl/Integrations/GuzzleFeatureRequester.php
index e012d582..5ddffa51 100644
--- a/src/LaunchDarkly/Impl/Integrations/GuzzleFeatureRequester.php
+++ b/src/LaunchDarkly/Impl/Integrations/GuzzleFeatureRequester.php
@@ -62,6 +62,10 @@ public function __construct(string $baseUri, string $sdkKey, array $options)
             'debug' => $options['debug'] ?? false,
             'base_uri' => $baseUri
         ];
+        $proxy = Util::httpProxy($options);
+        if ($proxy !== null) {
+            $defaults['proxy'] = $proxy;
+        }
 
         $this->_client = new Client($defaults);
     }
diff --git a/src/LaunchDarkly/Impl/Util.php b/src/LaunchDarkly/Impl/Util.php
index 0cfcefa0..b0a3b0f8 100644
--- a/src/LaunchDarkly/Impl/Util.php
+++ b/src/LaunchDarkly/Impl/Util.php
@@ -82,6 +82,27 @@ public static function logExceptionAtErrorLevel(LoggerInterface $logger, \Throwa
         );
     }
 
+    /**
+     * Reads the http_proxy option.
+     *
+     * A value that is not a non-empty string is ignored, so the proxy environment variables apply.
+     *
+     * @return ?string the proxy URL, or null if there is no valid value
+     */
+    public static function httpProxy(array $options): ?string
+    {
+        $proxy = $options['http_proxy'] ?? null;
+        if ($proxy === null || (is_string($proxy) && $proxy !== '')) {
+            return $proxy;
+        }
+
+        $logger = $options['logger'] ?? null;
+        if ($logger instanceof LoggerInterface) {
+            $logger->warning('The http_proxy option is not a non-empty string. The SDK ignores it.');
+        }
+        return null;
+    }
+
     public static function makeNullLogger(): LoggerInterface
     {
         return new Logger('', [new NullHandler()]);
diff --git a/src/LaunchDarkly/Integrations/Curl.php b/src/LaunchDarkly/Integrations/Curl.php
index 3d81480b..d2784715 100644
--- a/src/LaunchDarkly/Integrations/Curl.php
+++ b/src/LaunchDarkly/Integrations/Curl.php
@@ -25,6 +25,9 @@ class Curl
      * This implementation forks a process for each event payload. Alternatively, you can use
      * {@see \LaunchDarkly\Integrations\Guzzle::eventPublisher()}, which makes synchronous requests.
      *
+     * On Windows, this publisher does not use curl. It sends events with the PowerShell `Invoke-WebRequest`
+     * command, and it ignores the `curl` option.
+     *
      * @param array $options  Configuration settings (can also be passed in the main client configuration):
      *   - `curl`: command for executing `curl`; defaults to `/usr/bin/env curl`
      *   - `payload_temp_dir`: directory for the temporary file that holds the event payload. Use `true`
@@ -34,6 +37,9 @@ class Curl
      * with `Argument exceeds the allowed length of N bytes`. On Windows the payload always goes into a
      * file, and this option only names the directory; the default there is the system temporary
      * directory.
+     *   - `http_proxy`: URL of a web proxy for the requests; see {@see \LaunchDarkly\LDClient::__construct()}.
+     * On Windows, `Invoke-WebRequest` does not read credentials from the proxy URL. To use a proxy that
+     * requires authentication on Windows, use {@see \LaunchDarkly\Integrations\Guzzle::eventPublisher()}.
      * @return mixed  an object to be stored in the `event_publisher` configuration property
      */
     public static function eventPublisher(array $options = []): mixed
diff --git a/src/LaunchDarkly/Integrations/Guzzle.php b/src/LaunchDarkly/Integrations/Guzzle.php
index ba712832..0f8f229c 100644
--- a/src/LaunchDarkly/Integrations/Guzzle.php
+++ b/src/LaunchDarkly/Integrations/Guzzle.php
@@ -22,6 +22,7 @@ class Guzzle
      *   - `cache`: an optional object that implements `Kevinrob\GuzzleCache\Storage\CacheStorageInterface`
      *   - `connect_timeout`: connection timeout in seconds; defaults to 3
      *   - `timeout`: read timeout in seconds; defaults to 3
+     *   - `http_proxy`: URL of a web proxy for the requests; see {@see \LaunchDarkly\LDClient::__construct()}
      * @return mixed  an object to be stored in the `feature_requester` configuration property
      */
     public static function featureRequester(array $options = []): mixed
@@ -54,6 +55,7 @@ public static function featureRequester(array $options = []): mixed
      *   - `events_uri`: URI of the server that will receive events, if it is `ld-relay` instead of LaunchDarkly
      *   - `connect_timeout`: connection timeout in seconds; defaults to 3
      *   - `timeout`: read timeout in seconds; defaults to 3
+     *   - `http_proxy`: URL of a web proxy for the requests; see {@see \LaunchDarkly\LDClient::__construct()}
      * @return mixed  an object to be stored in the `event_publisher` configuration property
      */
     public static function eventPublisher(array $options = []): mixed
diff --git a/src/LaunchDarkly/LDClient.php b/src/LaunchDarkly/LDClient.php
index d545cebb..30ff149f 100644
--- a/src/LaunchDarkly/LDClient.php
+++ b/src/LaunchDarkly/LDClient.php
@@ -74,6 +74,12 @@ class LDClient
      * - `events_uri`: Base URI for sending events to LaunchDarkly. Change this if you are forwarding events through a Relay Proxy instance.
      * - `timeout`: The maximum length of an HTTP request in seconds. Defaults to 3.
      * - `connect_timeout`: The maximum number of seconds to wait while trying to connect to a server. Defaults to 3.
+     * - `http_proxy`: Use a proxy when the SDK connects to LaunchDarkly. This is the full URL of the proxy, for example
+     * `http://my-proxy.com:1234` or `http://user:pass@my-proxy.com:1234`. The SDK uses the proxy for HTTP and HTTPS
+     * targets. This option overrides the `HTTPS_PROXY` and `HTTP_PROXY` environment variables, but only for SDK
+     * connections. The `NO_PROXY` environment variable still applies, because libcurl reads it. On Windows, the
+     * default event publisher uses PowerShell, which does not read credentials from the proxy URL. See
+     * {@see \LaunchDarkly\Integrations\Curl::eventPublisher()}.
      * - `cache`: An optional implementation of Guzzle's [CacheStorageInterface](https://github.com/Kevinrob/guzzle-cache-middleware/blob/master/src/Storage/CacheStorageInterface.php).
      * Defaults to an in-memory cache.
      * - `send_events`: If set to false, disables the sending of events to LaunchDarkly. Defaults to true.
diff --git a/tests/Impl/Integrations/CurlEventPublisherTest.php b/tests/Impl/Integrations/CurlEventPublisherTest.php
index 1410ad23..069f30ce 100644
--- a/tests/Impl/Integrations/CurlEventPublisherTest.php
+++ b/tests/Impl/Integrations/CurlEventPublisherTest.php
@@ -159,4 +159,33 @@ public function testRemovesPayloadFileAfterTheRequest()
 
         $this->assertEmpty(glob($dir . '/ld-*') ?: []);
     }
+
+    public function testPassesHttpProxyToCurl()
+    {
+        $publisher = $this->makePublisher(['http_proxy' => 'http://user:pass@my-proxy:8080']);
+        $this->assertTrue($publisher->publish(self::PAYLOAD));
+
+        $args = $this->awaitRecordedArgs();
+        $index = array_search('--proxy', $args, true);
+        $this->assertNotFalse($index);
+        $this->assertEquals('http://user:pass@my-proxy:8080', $args[$index + 1]);
+    }
+
+    public function testDoesNotPassProxyByDefault()
+    {
+        $this->assertTrue($this->makePublisher()->publish(self::PAYLOAD));
+
+        $this->assertNotContains('--proxy', $this->awaitRecordedArgs());
+    }
+
+    /**
+     * @testWith [false]
+     *           [""]
+     */
+    public function testIgnoresInvalidHttpProxy(mixed $proxy)
+    {
+        $this->assertTrue($this->makePublisher(['http_proxy' => $proxy])->publish(self::PAYLOAD));
+
+        $this->assertNotContains('--proxy', $this->awaitRecordedArgs());
+    }
 }
diff --git a/tests/Impl/Integrations/EventPublisherTest.php b/tests/Impl/Integrations/EventPublisherTest.php
index b04b1428..5de10e49 100644
--- a/tests/Impl/Integrations/EventPublisherTest.php
+++ b/tests/Impl/Integrations/EventPublisherTest.php
@@ -51,6 +51,63 @@ public function getEventPublisher(): array
         ];
     }
 
+    public function getProxiedEventPublisher(): array
+    {
+        /** @var LoggerInterface **/
+        $logger = $this->getMockBuilder(LoggerInterface::class)->getMock();
+
+        // The host does not resolve, so the request can only arrive through the proxy.
+        $config = [
+            'events_uri' => 'http://not.valid.local',
+            'timeout' => 3,
+            'connect_timeout' => 3,
+            'logger' => $logger,
+            'http_proxy' => 'http://localhost:8080',
+        ];
+
+        return [
+            [new Integrations\CurlEventPublisher('sdk-key', $config)],
+            [new Integrations\CurlEventPublisher('sdk-key', array_merge($config, ['payload_temp_dir' => true]))],
+            [new Integrations\GuzzleEventPublisher('sdk-key', $config)],
+        ];
+    }
+
+    /**
+     * @dataProvider getProxiedEventPublisher
+     */
+    public function testSendsThroughHttpProxy($publisher)
+    {
+        $event = json_encode(["key" => "user-key"]);
+        $publisher->publish($event);
+
+        $requests = [];
+        $client = new Client();
+
+        // Provide time for the curl to execute
+        $start = time();
+        while (time() - $start < 5) {
+            $response = $client->request('GET', 'http://localhost:8080/__admin/requests');
+            $body = json_decode($response->getBody()->getContents(), true);
+            $requests = $body['requests'];
+
+            if ($requests) {
+                break;
+            }
+            usleep(100);
+        }
+
+        if (!$requests) {
+            $this->fail("Unable to connect to endpoint within specified timeout");
+        }
+
+        $this->assertCount(1, $requests);
+
+        $request = $requests[0]['request'];
+        $this->assertEquals($event, $request['body']);
+        $this->assertEquals('/bulk', $request['url']);
+        $this->assertEquals('not.valid.local', $request['headers']['Host']);
+    }
+
     /**
      * @dataProvider getEventPublisher
      */
diff --git a/tests/Impl/Integrations/GuzzleFeatureRequesterTest.php b/tests/Impl/Integrations/GuzzleFeatureRequesterTest.php
index da98eee3..682f1c58 100644
--- a/tests/Impl/Integrations/GuzzleFeatureRequesterTest.php
+++ b/tests/Impl/Integrations/GuzzleFeatureRequesterTest.php
@@ -77,6 +77,49 @@ public function testSendsCorrectHeaders(): void
         $this->assertEquals('my-instance-id', $headers['X-LaunchDarkly-Instance-Id']);
     }
 
+    public function testSendsRequestThroughHttpProxy(): void
+    {
+        /** @var LoggerInterface **/
+        $logger = $this->getMockBuilder(LoggerInterface::class)->getMock();
+
+        $config = [
+            'logger' => $logger,
+            'timeout' => 3,
+            'connect_timeout' => 3,
+            'http_proxy' => 'http://localhost:8080',
+        ];
+
+        // The host does not resolve, so the request can only arrive through the proxy.
+        $requester = new GuzzleFeatureRequester('http://not.valid.local', 'sdk-key', $config);
+        $requester->getFeature("flag-key");
+
+        $requests = [];
+        $client = new Client();
+
+        // Provide time for the curl to execute
+        $start = time();
+        while (time() - $start < 5) {
+            $response = $client->request('GET', 'http://localhost:8080/__admin/requests');
+            $body = json_decode($response->getBody()->getContents(), true);
+            $requests = $body['requests'];
+
+            if ($requests) {
+                break;
+            }
+            usleep(100);
+        }
+
+        if (!$requests) {
+            $this->fail("Unable to connect to endpoint within specified timeout");
+        }
+
+        $this->assertCount(1, $requests);
+
+        $request = $requests[0]['request'];
+        $this->assertEquals('/sdk/flags/flag-key', $request['url']);
+        $this->assertEquals('not.valid.local', $request['headers']['Host']);
+    }
+
     public function wrapperProvider(): array
     {
         return [