The latest publication from the Aspen Institute's Program on Philanthropy and Social Innovation, Time is of the Essence: Foundations and the Policies of Limited Life and Endowment Spend-Down combines detailed analysis of two famous historic foundations (Rosenwald Fund and General Education Board) with case studies of selected contemporary foundations (Lucille P. Markey Charitable Trust, Corella and Bertram F. Bonner Foundation, and Mary Flagler Cary Charitable Trust) that decided to spend down their assets within a set period of time instead of existing in perpetuity. Written by John R. Thelin (University of Kentucky) and Richard Trollinger (Centre College), this publication provides donors and foundations with models for consideration in their own policies and planning in the 21st century.