This book presents a broad coverage of the principles and recent developments of sample preparation and fractionation tools in Expression Proteomics in general and for two-dimensional electrophoresis (2-DE) in particular. 2-DE, with its unique capacity to resolve thousands of proteins in a single run, is still a fundamental research tool for nearly all protein-related scientific projects. The methods described here in detail are not limited to 2-DE and can also be applied to other protein separation techniques.