Abstract: “Superconducting radio frequency (SRF) cavities are an enabling technology for all modern accelerators where they serve as a primary means to accelerate charged beams. Extremely high quality factors Q=10^10-10^11 of SRF cavities in the broad range of fields up to tens of MV/m allow continuous wave operation of accelerators for various applications, i.e. SNS, CEBAF, LCLS-II, PIP-II and others, as well as make SRF cavities an attractive option for various non-accelerator applications ranging from quantum computing to dark sector photon searches. In this talk I will review the underlying science achievements and challenges in SRF, as well as describe the new SRF ‘quantum’ regime effort at Fermilab.”