You can use Amazon S3's REST-based interface to upload and download objects. Unity doesn't support PUT requests, but it does support GET and POST requests, and those are sufficient for reading and writing. You'll use the WWW class for this, with the three-argument form: The first argument will be the S3 URL, the second will be the file contents encoded as a byte array, and the third will be a hashtable of the form fields. More info on the WWW class is in the Unity script reference, and documentation of the REST API for S3 is here. In particular, note the link about POST-based uploads.