The main objective of the book is to present the recent development of the fast tuner attached to TESLA type cavities assembled in FLASH accelerator at Deutsche Elektronen-Synchrotron (DESY) laboratory in Hamburg, Germany. The book is organized in 7 chapters. General accelerator technology are presented in introduction. Moreover, the TESLA type cavity and its tuning system is presented in details. Beside of that, thesis also covers the information about alternative development of tuners, which might be used for TESLA type cavities for future machines. Chapter 3 summarizes the information about detuning sources and the methods of its compensation. In chapter 4 the smart materials, which might be used for fast tuning system, are presented. Especially, there results of experiments performed at cryogenic and room temperature of piezoelectric stacks from five different manufacturers and two types of magnetostrictive rods are shown. The innovative method of using the active element itself to estimate the preload is presented in Chapter 5. Next chapter is dedicated to the fast tuning system used for FLASH accelerator. The book is finished with two appendixes.