Supports GET, HEAD, POST, DELETE, PUT, and OPTIONS
Allows full access to request and response headers
Persistent connections are implicitly managed by Guzzle, resulting in huge performance benefits
Send requests in parallel
Cookie sessions can be maintained between requests using the CookiePlugin
Allows custom entity bodies to be sent in PUT and POST requests, including sending data from a PHP stream
Responses can be cached and served from cache using the caching reverse proxy plugin
Failed requests can be retried using truncated exponential backoff
Entity bodies can be validated automatically using Content-MD5 headers
All data sent over the wire can be logged using the LogPlugin
Automatically requests compressed data and automatically decompresses data
Subject/Observer signal slot system for unobtrusively modifying request behavior
Supports all of the features of libcurl including authentication, redirects, SSL, proxies, etc
Web service client framework for building future-proof interfaces to web services

HTTP basics

<?php

use Guzzle\Service\Client;

$client = new Client('http://www.example.com/api/v1/key/{{key}}', array(
    'key' => '***'
));

// Issue a path using a relative URL to the client's base URL
// Sends to http://www.example.com/api/v1/key/***/users
$request = $client->get('users');
$response = $request->send();

// Relative URL that overwrites the path of the base URL
$request = $client->get('/test/123.php?a=b');

// Issue a head request on the base URL
$response = $client->head()->send();
// Delete user 123
$response = $client->delete('users/123')->send();

// Send a PUT request with custom headers
$response = $client->put('upload/text', array(
    'X-Header' => 'My Header'
), 'body of the request')->send();

// Send a PUT request using the contents of a PHP stream as the body
// Send using an absolute URL (overrides the base URL)
$response = $client->put('http://www.example.com/upload', array(
    'X-Header' => 'My Header'
), fopen('http://www.test.com/', 'r'));

// Create a POST request with a file upload (notice the @ symbol):
$request = $client->post('http://localhost:8983/solr/update', null, array (
    'custom_field' => 'my value',
    'file' => '@/path/to/documents.xml'
));

// Create a POST request and add the POST files manually
$request = $client->post('http://localhost:8983/solr/update')
    ->addPostFiles(array(
        'file' => '/path/to/documents.xml'
    ));

// Responses are objects
echo $response->getStatusCode() . ' ' . $response->getReasonPhrase() . "\n";

// Requests and responses can be cast to a string to show the raw HTTP message
echo $request . "\n\n" . $response;

// Create a request based on an HTTP message
$request = RequestFactory::fromMessage(
    "PUT / HTTP/1.1\r\n" .
    "Host: test.com:8081\r\n" .
    "Content-Type: text/plain"
    "Transfer-Encoding: chunked\r\n" .
    "\r\n" .
    "this is the body"
);

Send requests in parallel

<?php

use Guzzle\Service\Client;

try {
    $responses = $client->batch(array(
        $client->get('http://www.google.com/'),
        $client->head('http://www.google.com/'),
        $client->get('https://www.github.com/')
    ));
} catch (PoolRequestException $e) {
    echo "The following requests encountered an exception: \n";
    foreach ($e as $exception) {
        echo $exception->getRequest() . "\n" . $exception->getMessage() . "\n";
    }
}