This paper delves into the concept of co-design, a collaborative approach involving stakeholders in the conceptualization and design phases to understand diverse perspectives and jointly define project directions. Examining the relationships between co-design, Design Thinking, and user-centred design, the paper emphasises distinctions in their goals and methods. It addresses potential biases in co-design processes, providing strategies to mitigate analogical relations, cognitive effort minimization, and emotional influences. Epistemological reflections highlight the efficacy of participatory methods in generating theoretical hypotheses while underscoring the need for evidence-based validation. The article explores co-design’s applications in speculative design and ludo-didactics (game design). In speculative design, co-design aids in framing problems and generating plausible contextualizations, while in game design, participatory processes, particularly playtesting, enhance the exploratory and refinement phases. The paper suggests avenues for further research, emphasising the strategic placement of Co-design processes in project phases, considering potential biases, and exploring its application in disruptive innovation contexts.