diff --git a/README.md b/README.md
index 55ddfda..57ff6c8 100644
--- a/README.md
+++ b/README.md
@@ -23,7 +23,15 @@ curl -sS https://getcomposer.org/installer | php
 
 # Add Mailgun as a dependency
 php composer.phar require mailgun/mailgun-php:~1.7.2
-``` 
+```
+
+You do also need to choose what library to use when you are sending messages. Consult the
+[php-http/adapter-implementation](https://packagist.org/providers/php-http/adapter-implementation) virtual package to
+find adapters to use. Example:
+
+```bash
+php composer.phar require php-http/guzzle6-adapter:^0.1.0
+```
 
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