Much of the pioneering early pulsed EPR was conducted in the group of W. B. Mims at Bell Labs during the 1960s. In the first decade only a small number of groups worked the field, because of the expensive instrumentation, the lack of suitable microwave components and slow digital electronics. The first observation of electron spin echo envelope modulation (ESEEM) was made in 1961 by Mims, Nassau and McGee. Pulsed electron nuclear double resonance (ENDOR) was invented in 1965 by Mims. In this experiment, pulsed NMR transitions are detected with pulsed EPR. ESEEM and pulsed ENDOR continue to be important for studying nuclear spins coupled to electron spins.