Foundations set out ambitious goals in their quest to improve the wellbeing of individuals and societies.  Philanthropic leaders are increasingly aware that to achieve the large-scale impact that they seek, they need to focus on a specific problem and intentionally and coherently approach it from multiple directions. In supporting a diversity of strategies to catalyze and sustain systemic change, foundations often build fields.  Foundations have both helped stimulate work in new fields and supported existing fields.  This paper defines a field, provides examples of how funders build fields, lists the elements of a strong field, and discusses effective donor practices to promote sustainable fields.  The paper concludes with questions that can help to assess field strengths and needs, and a discussion of the best time to exit a field.

This paper is based on a study for the Robert Wood Johnson Foundation conducted in 2011 by the same author that resulted in a report titled Exiting Responsibly: Best Donor Practices in Ending Field Support.