According to the 'internal marketing' (IM) concept, companies can improve the quality of their goods and services via more satisfied employees. Employees should be considered as internal customers and without doubt customers should be treated well. In order to do that, companies should adopt a marketing-like internal approach and apply marketing-like activities internally. Despite definitions for the concept have proliferated and its content has expanded considerably in the last two decades, actually few companies were able to benefit internal marketing in practice enough. That may partly be due to the confusion, vagueness and differentiation seen in the development of the IM concept. This study aims to review definitions, development, causes, problems and some models of internal marketing. Besides, a specific emphasis is given to the link between internal and external customer satisfaction, and the dimensions used to evaluate internal service quality.