This book constitutes the refereed proceedings of the Third International Symposium on Unifying Theories of Programming, UTP 2010, held in Shanghai, China, in November 2010, in conjunction with the 12th International Conference on Formal Engineering Methods, ICFEM 2010. The 12 revised full papers presented together with 3 invited talks were carefully reviewed and selected from 25 submissions. Based on the pioneering work on unifying theories of programming of Tony Hoare, He Jifeng, and others, the aims of this Symposium series are to continue to reaffirm the significance of the ongoing UTP project, to encourage efforts to advance it by providing a focus for the sharing of results by those already actively contributing, and to raise awareness of the benefits of such a unifying theoretical framework among the wider computer science and software engineering communities.