Peptidomics is the study of endogenous peptides in biological samples. It analyzes peptides on a larger scale than proteomics due to peptides' lower molecular weight and higher numbers produced through proteolytic processing. Peptidomics can detect markers not accessible by proteomics as peptides reflect protease activity. The process involves fractionating samples, analyzing peptides by mass spectrometry, and correlating peptide signals to variables like disease markers. Key factors for successful peptidomics studies include design, quality control, technology integration, and a holistic biological and technical approach.