From CERN Courier, Nov. 10, 2020: Established 30 years ago with a linear electron-positron collider in mind, the TESLA Technology Collaboration has played a major role in the development of superconducting radio-frequency cavities and related technologies for a wide variety of applications. The first decade of the 21st century saw the TTC broaden its reach, for example, gradually opening to the community working on proton superconducting cavities, such as the half-wave resonator string collaboratively developed at Argonne National Lab and now destined for use in PIP-II at Fermilab.