Including frail older people in the development and improvement of healthcare is a topical issue and co-production represents a common approach. How to practice co-production effectively, however, remains challenging, particularly when including vulnerable populations. This paper provides methodological highlights from a project designed to improve care pathways for frail older people. The project applied a co-constructive approach to co-production using situated interviews. We make four recommendations for practice and two linked conclusions -that situated interviews represent a flexible and accessible method for engaging vulnerable populations and that conceptual clarity is essential to the delivery of effective co-production.