This book offers a comprehensive overview of the microstructures of Ti Ni based shape memory alloys. It begins by outlining essential specimen preparation and observation techniques for microstructural analysis, drawing on the authors' experience and unpublished data. Using these approaches, the book presents key observations of twin morphologies and interfacial structures, explains the rational but complex self accommodation architecture, and discusses transformation induced dislocations. The microstructures of practical alloys, shaped by processing and heat treatment, are also described in detail. In situ SEM studies further illustrate the nucleation and growth of monoclinic and trigonal martensites, the formation of self accommodation structures, and the multistage transformation sequence characteristic of aged Ni rich alloys. The final two chapters address hydrogen effects relevant to medical applications and, separately, examine nonmetallic inclusions that influence device durability. This book serves students, materials scientists, and engineers engaged in research and development of Ti Ni based and other shape memory alloys.