This second part of the article on nuclear magnetic resonance considers systems which produce narrow resonance lines. The origins of line splitting are first considered, one type due to the chemical environment and a second type due to interaction between the nuclear spins within the molecule itself. The technique of double resonance simplifies complex spectra by applying a second radiofrequency at the same time. After a brief summary of results obtained from metals and ferromagnetics, the more recent Overhauser effects are described since the effective sensitivity of nuclear resonance spectrometers can be increased by several orders of magnitude by applying microwave power at the electron resonance frequency at the same time. The final section of the article considers echo and pulse techniques, and the way in which these can be applied in very low magnetic field strengths.