Over the past 8 years of programing Python professionally, I've used a bunch of concurrent/parallel APIs. I've written at least three concurrent APIs myself and influenced a few others. By far the most important part of these APIs is fan-out and fan-in. But these crucial components are not very much appreciated. Most people don't even realize they're there. The goal of this talk is to make you care about fan-out and fan-in, and see how the future of Python is bright in this regard. I'll explain what fan-out and fan-in are, and why they're useful. I'll go over a bunch of examples of fan-out and fan-in, including data constructs (ORMs like SQLAlchemy, Map Reduce, real-time aggregation), mutiple threads (subprocesses, queues, and [multiprocessing](http://docs.python.org/dev/library/multiprocessing.html)), and "futuristic" asynchronous APIs ([App Engine NDB](https://developers.google.com/appengine/docs/python/ndb/async), [Tulip/PEP3156](http://www.python.org/dev/peps/pep-3156)). Attendees will learn the value of fan-in and fan-out in API design. They'll have a name to give something they've used many times in their concurrent programs without realizing what the magical mechanisms are called. They'll get excited about the future of Python because Tulip/PEP3156 is such a great API for concurrency.