Since the arrival of high temperature superconductivity in 1987, the measurement of ac susceptibility has gradually become more popular as a large number of laboratories around the world have either already acquired an ac susceptometer or are in the process of doing so. Its advantage over other techniques is that it is an inductive, noncontact measurement that screens an entire volume of the sample. Here it is explained why this seemingly simple technique is very useful and the principle of measurement is explained in full detail. It is shown how to design and construct a low‐cost susceptometer and how to interpret the data when applied to high temperature bulk superconductors.