The main emphasis of this book is on the practical application of unitary transformations to problems in solid state physics. This is a method used by the author and his collaborators for years in the field of nonadiabatic electron-phonon phenomena where the Born-Oppenheimer approximation is no longer applicable. This book is intended as a tool for those who want to apply unitary transformations quickly and on a more elementary level and also for those who want to use this method for more involved problems. ``Unitary Transformations in Solid State Physics'' is divided into 6 chapters. The first three chapters are concerned with presenting quick applications of unitary transformations and chapter 4 presents a more systematic procedure. The last two chapters contain the major known examples of the utilization of unitary transformations in solid state physics, including such highlights as the Frohlich and the Fulton-Gouterman transformations. The book is supplemented by extended tables of unitary transformations, whose properties and peculiarities are also listed.