Book excerpt: This book provides a comprehensive overview of Expressed Protein Ligation (EPL), detailing methods and protocols to generate site-specifically modified proteins. Chapters include an overview of the protein semi-synthesis field, as well as related areas that have contributed to the development of EPL such as protein splicing and peptide synthesis. Following the introductory chapters, the rest of the book guides readers through protocols to perform EPL reactions, methods to synthesize peptide thioesters and to perform peptide and protein ligations, label proteins inside living cells, protocols for the semi-synthesis of phorphorylated, glycosylated and ubiquitylated proteins, synthesis and assembly of assymetrically modified nucleosomes, use of ligation auxiliaries and synthesis of cyclic proteins, as well as novel desulfurization strategies and use of selective Cys side chain protection to obtain precisely modified proteins.Written in the highly successful Methods in Molecular Biology series format, chapters include introductions to their respective topics, lists of the necessary materials and reagents, step-by-step, readily reproducible laboratory protocols, and tips on troubleshooting and avoiding known pitfalls. Authoritative and cutting-edge, Expressed Protein Ligation: Methods and Protocols will ensure successful implementation of protein semi-synthesis methods to further study the structure and function of proteins.