Peptides represent a fast-moving frontier in biomedical research. Many peptides function as signaling molecules they bind to receptors and influence processes such as hormone release, appetite regulation, inflammation, tissue repair, and cellular stress responses. Because signaling pathways can be highly specific, peptides are often discussed as “targeted” compared with broad-acting drugs. This ebook focuses on the science of how peptides work, how they are commonly classified, where evidence is strong vs uncertain, and how to think about safety and decision-making responsibly.