Antibody–drug conjugates (ADCs) seek to exploit the desirable features of their components, i.e., specificity in targeting tumor cells and long half-life in plasma conferred by the antibody, and the cytotoxic potency of the small effector molecule. A linker tethers the antibody to a cytotoxic agent and allows stable circulation of the cytotoxin in the form of pro-drug. Many linkers have been designed over the years and have showcased features that are more than a mere physical linkage between the two constituent parts. Linkers can confer several advantages to ADCs, such as modulating the rate of cytotoxin release in tumor cells, overcoming multidrug resistance, enhancing tumor penetration, and a better safety profile in humans. This review highlights the progress made in linker technology and how it has impacted the design of optimal ADCs for clinical evaluation.