Antibody–drug conjugates (ADCs) are therapeutic agents in which highly potent cytotoxic small molecules are covalently attached to monoclonal antibodies via chemical linkers (Fig. 114.1). Currently, more than 10 ADCs have been approved for clinical use, primarily for cancer therapy. The fundamental concept of ADCs is to harness the antigen-specific binding ability of antibodies to selectively deliver cytotoxic payloads to diseased tissues, where they are released at the target site. This strategy enables expansion of the therapeutic window by maximizing efficacy while minimizing off-target toxicity to healthy tissues.