Abstract Motivation: Addressing today’s social, environmental, and technological challenges requires not only strong strategies but also approaches that coordinate stakeholder activities across ecosystems. While many tools help multi-stakeholder partnerships analyze the past and envision desirable futures, stakeholders often struggle to translate those visions into actionable steps because their goals and values in the present are misaligned. This misalignment leads to planning paralysis or fragmented efforts. The Collective Action Planning (CAP) method: CAP is a facilitation method that integrates diverse stakeholder goals and perspectives to create complementary, actionable solutions. Grounded in systems thinking and pragmatism – particularly the concept of simplexity, which balances complex understanding with simple action – CAP connects requirements, constraints, and activities across ecosystems, emphasizing how pilot experiments interact with existing structures. Research Design: Developed through an echeloned Design Science Research (eDSR) process involving sixteen validation cycles in seminars, trainings, and projects, CAP now comprises five steps. Practitioner benefits: We illustrate CAP use through the case of building a circular ecosystem for reusable to-go cups. CAP enhances sensemaking and coordination in multi-stakeholder partnerships, helping actors move from shared vision to collective action – in short, it is a method for acting together.