The growth of Fourier Transform spectroscopy over the last two decades has been nothing short of astounding especially since it lay dormant for the 8 decades prededing this development. This delayed development is the direct result of the computational intensity of FTS compared to the relatively simple dispersive spectrometer. As a result many Fourier transform spectrometers are placed in labs and used by people who do not understand their operation. This is compounded by the sophisticated use of the computer by FTS. Understanding FTS is a difficult task because the concepts are alien to many and to complicate matters the mathematics involved are just as confusing. This book is written to address this problem directly. The functioning of the inferometer is presented as if it were constructed from dispersive components. This allows the strengths and weaknesses of FTS to be understood easily and completely. Similarly the Fourier transform itself is presented in a graphical rather than mathematical fashion so that it is easily grasped.