Objective. The aim of this study was to provide a critical understanding of the role of theories and their compatibility with a person-centered approach in the design and evaluation of web-based support for the management of chronic illness. Methods. Exploration of web-based support research projects focusing on four cases: (1) preschool children aged 4–6 with bladder dysfunction and urogenital malformation; (2) young adults aged 16–25 living with mental illness; (3) women with type 1 diabetes who are pregnant or in early motherhood; and (4) women who have undergone surgery for breast cancer. Data comprised interviews with research leaders and documented plans. Analysis was performed by means of a cross-case methodology. Results. The used theories concerned design, learning, health and well-being, or transition. All web support products had been developed using a participatory design (PD). Fundamental to the technology design and evaluation of outcomes were theories focusing on learning and on health and well-being. All theories were compatible with a person-centered approach. However, a notable exception was the relatively collective character of PD and Communities of Practice. Conclusion. Our results illustrate multifaceted ways for theories to be used in the design and evaluation of web-based support.