This book constitutes the thoroughly refereed post-proceedings of the First International Symposium on Unifying Theories of Programming, UTP 2006, held at Walworth Castle, County Durham, UK, in February 2006. The book presents 14 revised full papers. Based on the pioneering work on unifying theories of programming by Tony Haare and Jifeng He, UTP 2006 focused on the most significant results and raised awareness of the benefits of unifying theoretical frameworks.