Voltage stability is a problem in power systems, which are heavily loaded, faulted or have a shortage of reactive power. The nature of voltage stability can be analyzed by examining the production, transmission and consumption of reactive power. The problem of voltage stability concerns the whole power system, although it usually has a large involvement in one critical area of the power system. With the evolution of modern heavily compensated power systems, voltage stability has emerged as the limiting consideration in many systems. The phenomenon of voltage collapse is dynamic, yet frequently evolves very slowly, from the perspective of a transient stability program. The course aims to highlight the phenomena of voltage stability and factors lead to system collapse. The course will also discuss methods for problems remedy with examples.