This book describes the basic physical principles of techniques to generate and ultrashort pulse lasers and applications to ultrafast spectroscopy of various materials covering chemical molecular compounds, solid-state materials, exotic novel materials including topological materials, biological molecules and bio- and synthetic polymers. It introduces non-linear optics which provides the basics of generation and measurement of pulses and application examples of ultrafast spectroscopy to solid state physics. Also it provide not only material properties but also material processing procedures. The book describes also details of the world shortest visible laser and DUV lasers developed by the author's group. It is composed of the following 12 Sections: The special features of this book is that it is written by a single author with a few collaborators in a systematic way. Hence it provides a comprehensive and systematic description of the research field of ultrashort pulse lasers and ultrafast spectroscopy.