Guided by history, we review the major developments concerning realistic nucleon-nucleon (NN) potentials since the pioneering work by Kuo and Brown on the effective nuclear interaction. Our main emphasis is on the physics underlying various models for the NN interaction developed over the past quarter-century. We comment briefly on how to test the quantitative nature of nuclear potentials properly. A correct calculation (performed by independent researchers) of the χ 2 /datum for the fit of the world NN data yields 5.1, 3.7, and 1.9 for the Nijmegen, Paris, and Bonn potential, respectively. Finally, we also discuss in detail the relevance of the on-and off-shell properties of NN potentials for microscopic nuclear structure calculations.