Today, in this time of scarcity of conventional energy sources, photovoltaics is viewed as an ideal way to produce eco-friendly power. Cost of photovoltaic systems is a key factor affecting large-scale applications. However, improvements in conversion efficiency will help to reduce the cost. It is a challenge to develop new or improved thin-film materials with good photovoltaic properties. CuInS2 has great potential for photovoltaic applications. This book contains results of the work done in the Thin Film Photovoltaic Division of the Dept. of Physics, CUSAT and is organized into five chapters with introduction, conclusion and references. Chapter-1 is a general introduction to solar cells. It starts with a brief history of solar cells and describes principle and theory of solar cell operation. Chapter-2 presents an exhaustive review on Copper indium sulfide films and CuInS2 based solar cells. Chapters 3 and 4 mainly deal with the preparation and characterization of copper indium sulfide films using CBD copper sulfide films and chemical spray pyrolysis respectively. Fabrication of CuInS2/CdS solar cells by an “all-spray” method is described in Chapter-5.