Purpose – This paper aims to present the first systematic review of the literature relating to the relationships between organisations and their marketing agencies, the agency– client relationship, and presents a concept matrix that identifies the key areas of investigation, and topics where further research would be beneficial. As agencies play a pivotal role in operationalising marketing strategy, this relationship is central to marketing theory, management and practice. Design/methodology/approach – A systematic review of the literature was performed using key databases and search terms, and filtering on the basis of criteria relating, for example, to relevance and format, to create a core set of refereed papers on the agency– client relationship in the marketing and advertising domains. Bibliographic and thematic analysis was used to profile the literature in the dataset, and to draw out key themes. Findings – The paper provides an analysis of the extant knowledge base, including key themes, journals and research methods. The following themes emerged from the literature, and are used to elaborate further on the existing body of knowledge: conflict, client account management, contracts and agency theory, cultural and international perspectives and co-creation. An agenda for future research is proposed that advocates a focus on theoretical foundations, research strategies and research topics and themes. Originality/value – This is the first systematic review of the literature on agency– client relationships, which is scattered across disciplines and informed by several theoretical perspectives. Given the increasing complexity of agency– client relationships in the digital age, and increasing need to understand “marketing-as-practice”, the coherent overview offered by this paper is of particular value for guiding future research.