Summary: This paper begins by presenting the theory of boundary critique, which is a key aspect of current work in the area of critical systems thinking. The theory suggests that researchers should remain aware of the need to access a diverse variety of stakeholder views in defining problems, and to ‘sweep in’ relevant information. It also offers an understanding of how conflicts between stakeholders can become stabilised, leading to the marginalisation of some stakeholder groups and the issues that concern them. This indicates the importance of taking processes of marginalisation into account during interventions, promoting and revaluing the contributions that can be made by marginal groups. The theory of boundary critique is illustrated through a case study in which the researchers supported the multi-agency development of housing services for older people. Reflection upon this case study reveals that the principle means by which the theory of boundary critique informs intervention is through the design of methods. Methods can be developed specifically to explore the boundaries of problems. Also, the design of methods to address these problems can take account of the need to preserve the contributions of marginalised groups.