Laying the foundations of property rights economics stands out among Ronald Coase's many seminal contributions. This approach had an impact on a number of fields in economics in, particularly, the 1960s and 1970s. The modern body of property rights economics mainly originates in the work Oliver Hart and is quite different in style, scope, and implications from the original property rights economics of Coase, Demsetz, Alchian, Cheung, Umbeck, Barzel, etc. Based on our earlier work on the subject (Foss and Foss, 2001), we argue that the change from Mark I to Mark II property rights economics led to a substantial narrowing of the scope of property rights economics, somewhat akin to a Kuhnian loss of content. In particular, Mark II property rights economics make strong assumptions concerning the definition and enforcement of ownership rights made which lead to many real life institutions and governance arrangements being excluded from consideration, and a much more narrow focus than that of the rich institutional research program initiated by Coase and his followers.