This Element focuses on interactions between international assignees (IAs) and host country nationals (HCNs) by synthesizing three decades of empirical research using a combination of bibliometric, thematic, and content analyses. It delineates three major research streams in the field: language and communication; cultural adjustment; and IA-HCN relationships. Utilizing innovative mixed-methods review and analytical techniques, we shed light on the effects of language, communication, and cultural issues on IAs' and HCNs' adjustment, performance, learning, and career development. This Element reveals mixed effects of IA-HCN interactions, calling for further research to contribute to a more comprehensive understanding of IA-HCN interactions. It offers valuable insights into effective cultural adjustment strategies and guides the development of practices for managing international assignments and cultivating positive IA-HCN relationships.