This TTC Topical Workshop will address a spectrum of issues related to pushing the performance limits of superconducting RF cavities toward higher quality factors and accelerating gradients as well as to investigating SRF cavity performance new regimes (very low temperatures and/or gradients.) The agenda will include discussions of new results from advanced measurements, experimental work on new materials (thin films, multi-layer superconductors, Nb3Sn, MgB2, …), and the latest theoretical advances.