The development of knowledge-intensive business services in recent decades can be interpreted as one of the indicators of a transformation from an industrial economy into a knowledge-based one. Not only do quantitative measures, whether in the form of sales or employment figures (e.g. Chadwick, Glasson and Lawton Smith, 2008), undoubtedly show the expansion of these services; but also their characteristics make it clear that they significantly affect the formation and spread of knowledge throughout the economy. This article presents an analysis of the KIBS sector based on a literature review. In the first section, it presents the issues connected with defining and categorizing KIBS. In the second one, it shows the significance of this type of service, highlighting its influence on the innovativeness of the companies which it serves. The third section consists of a detailed review of the literature devoted to research on KIBS.