As not-for-profits increasingly take on big issues such as global warming and economic development, some are turning to “collective impact.” This cross-sector approach involves nonprofits, government, businesses and others working together to solve a specific problem. Collective impact adherents often cite five keys for success: a common vision, a shared measurement system, mutually reinforcing activities, continuous communication and a separate support organization. But before joining a group, understand that such endeavors can be complicated and time-consuming.