The advent of modern techniques of observation in the world of amateur astronomers increases their potential to participate efficently to scientific programs. In particular, spectrography is a new, quickly developing tool for amateur astronomers. Moreover, amateur astronomers have more and more possibilities to access telescopes with diameters above 50 cm, either in professional observatories or belonging to associations. These improvements allow professional and amateurs to undertake fruitful collaborations and common meetings. This book collects the lectures given by professional for amateur astronomers during a CNRS school. It focuses on spectroscopy, a budding domain for amateurs already extensively used by professionals. Basic principles of spectroscopy are described in a clear and precise way and applications to the Sun, Be stars, nebulae, and comets are successively exposed. A chapter is dedicated to the analysis of spectral data, to put practical spectroscopy within reach of amateur astronomers.