This 6-hour lecture will start with the basic principles of RF superconductivity. It follows an introduction to cavities - starting from Maxwell's equation, eigenmodes and characteristics of standard (TM-mode elliptical) accelerating cavities will be introduced. After an excursion to non-elliptical cavities, the lecture will introduce the technologies used to fabricate, treat and assemble superconducting RF cavities and the methods to test them, including specialized diagnostics. Performance limitations and their mitigation will be mentioned. An important chapter will be on power couplers, higher-order modes and their coupling and damping. Finally recent progress in cavity performance and future trends of developments in the field will be presented.