The metabolomeis the set of small molecular weight compounds found in biological fluids and metabolomics/metabonomics is known as the large-scale, qualitative, and quantitative study of all metabolites in a given biological system. It is a data-driven approach combining analytical chemistry, biostatistics, informatics, and biochemistry. It complements tools already available to biologists for the characterization of gene functions, that is, transcriptomics and proteomics. After having been mostly used by analytical chemists and chemometricians, metabolomics is now part of the tools available to biologists working in the fields of agronomy, environmental sciences, and medicine. The aim of this review is to address liquid chromatography coupled to mass spectrometry (LC/MS)-based metabolomics and its expected input to discovery and validation of biomarkers. It starts with an introduction of the concept of biomarker for medicine and drug discovery. LC/MS-based metabolomics is then detailed with a particular emphasis on analytical chemistry and statistics. Bioinformatics issues, which are mandatory to enable the large-scale exploitation of metabolomics data by biologists and clinicians, are at last addressed.