After the spherical theta pinch had been developed at the Institute of Applied Physics in Frankfurt, considerable progress in creating high efficiency and long lifetime plasma sources had been made. Several devices have been built to study the characteristics of the spherically confined plasma. Scaling rules and investigated setups are presented, showing devices with electron densities of up to some 10 23 m -3 , electron temperatures of several eV and confinement times of ~10 μs. Typical dimensions are: discharge vessel radius R = 10 cm, radius of the pinched plasma r = 2 cm, initial gas pressures of 1-200 Pa at currents of up to 35 kA and resonance frequencies of 10-40 kHz. During the harmonic discharge of the stored energy, the plasma periodically pinches and expands again as long as the current rise rate creates sufficient electrical field strengths for ionization, which allows for pinching sequences in the millisecond range. The principles, improvements, theoretical approaches, and applications including pulsed ion source, plasma ion stripping, and vacuum ultraviolet flash lighting are discussed.