The story of UNITAID begins with two world leaders but quickly becomes a lesson in popular philanthropy, involving millions of people each making a small contribution to a program aimed at treating and ultimately eliminating the threat of HIV/AIDS, tuberculosis and malaria in the developing world. In partnership with the Clinton HIV/AIDS Initiative (CHAI), UNICEF, and other organizations, UNITAID has pioneered techniques for raising massive amounts of money from a wide pool of donors. Launched as a crucial component of UNITAID's "MassiveGood" substantial national publicity and promotion campaign, Power in Numbers is an inspiring case study for anyone interested in social justice, public health, philanthropy, or fundraising.