"I'm not sure where protocols are, but I want to say that they're not APIs. An API is a "one way" in a sense that it's unilateral: en entity guides ways to interact with it. A protocol, I would assume is more "multilateral": it may be defined by one entity but can apply to very different entities. For example, when HTTP was written by TBL, it was not JUST to interact with *his* server, but to get data from *any* server. That said, it does not mean that APIs can eventually become protocol. For example, IIRC, that *almost* happend with Twitter API when Wordpress implemented it in a way that you could post content to a WP site using the same client used for Twitter." - Julien