Aims and objectives: This introductory article aims to set the scene for the special issue by discussing existing and future research directions on multiword units (MWUs) in multilingual speakers. It also outlines the purpose and structure of the special issue and presents the individual contributions. Design, data and analysis: The introductory article reviews the most relevant theoretical and methodological issues as well as the main research gaps related to the processing, learning, and use of MWUs in both mono- and multilingual speakers. In addition, it introduces the contributions to this volume and briefly presents the types of MWUs, the types of multilingual speakers and the data and methodologies that are in focus. Conclusions, originality and implications: The contributions in this special issue on different types of MWUs in different groups of multilingual speakers using different methodologies shed new light on open questions in various areas of multilingualism research, including psycholinguistic approaches to second-language learning and processing, contact linguistics as well as research on heritage speakers and language attrition. In this regard, the special issue contributes to a more complete and differentiated picture of the role of MWUs in multilingual speakers but also in language processing, learning, and use in general.