Learn to use WordPress’s built in functionality (especially the HTTP library) to integrate with external APIs. We’ll touch on properly caching results to keep your site fast, fault tolerance, and even how to handle those strange APIs that send you data when you didn’t send a request for it (PayPal IPNs anyone?). We’ll talk theory, but mostly we’ll look at plenty of code and walk through examples from plugins that you can constantly refer back to for example code.