The last five years have seen the first serious enforcement efforts by licensors of open source software, so we are truly at the dawning of the age of enforcement. But open source claims are not like other claims. Understanding the distinctions between open source software claims and other intellectual property claims is key to reacting to open source claims gracefully, effectively, and with a minimum of embarrassment and cost. This Article provides a survey of where we stand today and demonstrates how this area of law has developed. We will be soon nearing the point where catalogs of open source claims in articles like this one will no longer be sensible or useful, but for now, seeing where we have been neatly explains where we are.