The primary objective of this book is to provide updated knowledge of recent advances in proteomics research in various fields. The topics covered include, but are not limited to, proteomic analysis for microbiomes, specific cell types from heterogeneous tissues, body fluids, mitochondria, and environmental toxicology. Almost all proteomics techniques currently used in research have been reviewed in at least one chapter, including traditional one- or two-dimensional gel-based, gel-free shotgun, label-based or label—free quantitative, and array-based methods. In addition, although they are not the major focus of this book, proteomics-related bioinformatics tools such as database searching, data mining, data analysis, and gene pathway analysis are briefly covered. Additionally, this book contains chapters on some technical issues related to applying proteomics technologies to specific issues, such as sample preparation for removal of contaminants and depletion of highly abundant proteins. Collectively, these chapters provide a broad view of various technologies commonly used in proteomics research and their successful applications to address different questions across various species. It is our hope that such a book can provide readers with a comprehensive understanding of proteomics technologies and their application to address various scientific questions.