This book is intended especially for students and researchers working with generation, interpretation and applications of THz transition radiation. It concentrates in much detail on theoretical and experimental discussions of coherent THz femtosecond transition radiation from ultrashort electron pulses and will serve as a guide for experimental design to generate and characterize such radiation with detailed interpretations. Experimental results of non-destructive diffraction radiation are also discussed in much detail. In one of its applications, coherent transition radiation is being used for longitudinal beam diagnostics, especially bunch length measurement with femtosecond pulse resolution. Complete performance, analyses and limitations of bunch length measurements via the autocorrelation technique will be presented in this book. The feature of femtosecond THz pulse is exploited in an example application to material science measuring the complex dielectric constant of materials with discussion of its experimental setup and results. The possibility to create stimulated transition radiation will be introduced with experimental results to demonstrate its feasibility.