We have determined the structure and nature of 'discontinuities' in the interplanetary magnetic field at 1 AU in the period March 18 to April 9, 1971, by using high-resolution magnetic field measurements from Explorer 43. The discontinuities that were selected for this analysis occurred under a variety of interplanetary conditions at an average rate of 0.5/hour. This set does not include all discontinuities that were present, but the sample is large, and it is probably representative. Both tangential and rotational discontinuities were identified. Tangential discontinuities were observed every day, even among Alfv¿nic fluctuations. In particular, on one day during which Alfv¿nic fluctuations were intense and persistent in a high-speed stream, tangential discontinuities (TD's) were seen throughout the day at an average rate of 0.5/hour; rotational discontinuities (RD's) were also observed during this day at a higher than usual rate, the ratio of TD's to RD's being approximately one. The structure of most of the current sheets was simple and ordered; i.e., the magnetic field usually changed smoothly and monotonically from one side of the current sheet to the other. The thickness distributions of the TD's and RD's with very smooth current sheets were similar. The average thickness of the RD's was 1200 km (13 proton Larmor radii), and the average thickness of the TD's was 1300 km (12 proton Larmor radii).