Metabolomics is the methodology and theory to study the metabolome, including targeted approaches based on selected/multiple reaction monitoring (SRM/MRM) and untargeted approaches based on nuclear magnetic resonance (NMR) or mass spectrometry (MS). The metabolome contains all metabolites derived from sugars, lipids, proteins, and nucleic acids in a given biological system, tissue, cell, or body fluid in a metabolic network system. Metabolomic variations directly link to molecular mechanisms of a disease, reliable therapeutic targets, and effective biomarkers for prediction, diagnosis, and prognostic assessment of disease. This book presents new advances in the concept and methodology of metabolomics, as well as applications of metabolomics in the research and practice of medical and life sciences.