Recent progress on the phase stability, microstructural control and mechanical properties of Co-base superalloys strengthened by the γ’ (L12) phase is presented focusing on the recent discovery of the γ’ phase of Co3(Al, W), (J. Sato et al., Science 312 (2006) 90.) The phase stability of γ’ compounds of Co3Al, Co3W, Co3Ta and Co3(Al, W) is presented. The effects of alloying elements on the stability of the γ’ phase is also shown. Furthermore, the microstructural aspects of not only the γ’ phase but also some other carbides and intermetallic compounds are shown. The development of new types of wrought and cast Co-base superalloys designed using the Calphad approach and microstructural control will also be presented.