Peptides control many biological processes, including cell-cell signaling as peptide hormones and neuropeptides, and within the cell in other capacities. Peptidomics is defined as the identification of peptides present in a biological sample. Although peptidomics is related to proteomics (the analysis of proteins), there are some distinct differences between these techniques in terms of overall goals and methodology. Most peptidomic studies are aimed at identifying the precise endogenous form of each peptide, including posttranslational modifications, whereas proteomic studies are usually focused on only identifying the proteins and not the precise forms. Quantitative peptidomics involves both the identification and quantification of peptide present in a sample, either by measuring the total levels of a peptide (absolute quantification) or by comparing peptide levels between different samples (relative quantification). In this review, we discuss the various techniques for quantification of peptides/proteins and their advantages and disadvantages with respect to their application in peptidomics.