This paper provides a systematic literature review and a future research agenda on the topic of purchasing of business services (BuSe). BuSe purchasing has increasingly gained in importance during the past years. It has established itself as a relevant sub-discipline in purchasing and supply management. This "state of research" paper identifies the main authors, relevant topics and practical implications as well as upcoming developments. For this purpose, 118 publications were collected and analyzed. While early research on BuSe purchasing was strongly influenced by the American marketing literature, more recent papers are also published by European authors and institutions coming from the core of the purchasing and supply management discipline. In general, the literature lacks in theoretical foundation and longitudinal methods while assuming high generalizability. Based on the analyses and additional discussions within the research team, directions for future research are identified at a political, economic, social and technological (PEST) level. The following trends for service purchasing were elaborated: (1) "Glocalisation" and nearshoring, (2) sustainability and corporate social responsibility (CSR), (3) internal and external collaboration, (4) value-driven contract and payment systems, (5) hybrid products and servitization, and (6) big data analytics, artificial intelligence and process automation.