Companies don’t win by isolating themselves, but they don’t win by overcollaborating, either. The real advantage comes from knowing what to build together and what to keep for yourself. It makes sense to collaborate on the “core”—things like infrastructure, standards, and trust, which allow an ecosystem to function—and to compete on the “edges”—those activities that allow companies to differentiate themselves. This article introduces a practical framework leaders can use to determine the right collaboration strategy. It includes five factors: market dynamics, technology life-cycle stage, your position in the technology stack, the level of competition, and social acceptance and regulation. By weighing each factor, leaders can devise a collaboration strategy that grows the market without giving away their edge.