An overview is given of collisional energy transfer measurements made in uniform supersonic flows. The fundamentals of molecular collisions and electronic, vibrational, and rotational energy transfer are briefly described, followed by a summary of the collisional systems that have been studied to date. The measurement of total and state-to-state collisional rate constants and cross sections is described and illustrated by reference to case studies for rotational, vibrational, and electronic energy transfer. These experimental data are critical for radiative transfer modeling of astrophysical environments as well as for fundamental tests of theoretical calculations. © 2022 by World Scientific Publishing Europe Ltd.