A number of methods exist for valuing a patent in order to license it to an external party. Several of these methods are well accepted in academic circles, others are merely tolerated as expedient. None of the existing methods, however, appears poised to easily accommodate software patent valuation in the face of open source software. Open source software distributors do not earn revenues directly from licensing source code. Even forprofit open source enterprises, such as Red Hat, provide software as part of a service bundle, not as an individually priced product. The problem of linking a patent to a stream of revenue generated by a bundle of goods holds for many service-oriented businesses, with open source as an extreme case. The increasing prevalence of service-based business models suggests that new thinking about how to put a price on patented innovations may be required. In addition to the basic problem of placing a dollar value on an innovation, new thinking on the incentives at play in license negotiations may also be necessary. In other words, do any unique principal-agent problems between patent holder and licensee surface as a result of the open source business model‘ Do any other licensing structure issues need to be worked through in order for existing theory to fit an open source environment. Before any of this 'new thinking' can begin (or is even warranted), though, an assessment of the current state of art is in order. This paper reviews the academic literature on valuing patent licenses.