The term peptide is typically used for polypeptides in the range up to approximately 20 kDa molecular weight. The origin of the term “peptide” (derived from the Greek terms „ peptos”, meaning digestible, and “poly-”, referring to its composition of two or more amino acids) reflects the fact that peptides are usually the products of proteolytic cleavage events . Many pathological processes are associated with changes in protease expression or activation and these changes are captured or represented in altered peptide profiles. Peptidomics® is defined as the systematic, comprehensive, qualitative and quantitative multiplex (e.g. mass spectrometry) analysis of endogenous peptides in a biological sample.