Undergraduate research (UR) is regarded as an impactful instructional practice, but implementing it in the curriculum is challenging. Faculty members' approaches to the design of UR are under-explored due to the scarcity of studies that situate practices in both the curricular contexts and the concept of the research-teaching nexus. This multiple-case study investigated faculty members' approaches to UR in four curricula in two research-intensive universities in Hong Kong. Document review and semi-structured interviews revealed five approaches to UR: project-based, process-based, lab-based, scenario-based, and research community-based approaches. Particularly, the scenario-based and research community-based approaches complemented the current typologies. Another contribution of this study is the identification of nuanced differences in the adoption of the approaches. Faculty members perceiving reciprocal research-teaching nexus at both departmental and personal levels, and viewing UR holistically, tended to connect students with their own research experiences. In contrast, those who only acknowledged the research-teaching nexus at a departmental level were unlikely to create such a connection. Meanwhile, concerns over curricular coherence and ethics were also discussed. The implications include creating a more transparent process of curriculum design and facilitating students' understanding of their contributions to the research community. It would also be useful to engage faculty members more fully in curriculum planning to enhance the coherence of students' research experiences.