In‐situ measurements of the solar wind began with simple ion traps on Soviet spacecraft in 1959. It wasn’t, however, until 1962 that the major properties of the solar wind were determined by Mariner 2. Improvements in instrumentation since then include the use of particle detectors, extension of the observations of the solar wind velocity vector to 2 or 3 dimensions, better time and energy resolution, greater variety of measurement locations, multipoint measurements, electron measurements, and the use of mass spectrometers and sample returns. This review summarizes what was learned about the solar wind from each of these improvements in instrumentation. © 2003 American Institute of Physics