Spree API Guide
This site covers the inner working of Spree's RESTful API. It assumes a basic understanding of the principles of REST.
The REST API is designed to give developers a convenient way to access data contained within Spree. With a standard read/write interface to store data, it is now very simple to write third party applications (eg. iPhone) that can talk to your Spree store. It is also possible to build sophisticated middleware applications that can serve as a bridge between Spree and a warehouse or inventory system.
For a comprehensive list of API functions, start browsing the resources in the above diagram.