This text and its companion volume "Protein Expression: A Practical Approach" form the final part of the PAS mini-series on protein synthesis and processing. This volume begins with a chapter on protein sequencing followed by a chapter on protein folding and import into organelles. The next three chapters cover the three major forms of covalent modification: phosphorylation, glycosylation, and lipid modification. Proteolytic processing is the next topic and the final two chapters are concerned with protein turnover in mammalian cells and yeast. This book is a comprehensive volume of late-1990s methodology and is designed to be used at the bench or away from the bench to gain insight into future experimental approaches.; This book is intended for any biomedical researcher wanting to investigate protein expression in cell free systems, viruses, prokaryotic cells, and eukaryotic cells.