The 2009 TIME 100

In 1976, a young Philadelphia nun named Sister Mary Scullion began her work as an advocate for the homeless, driven by a personal conviction that "none of us are home until all of us are home." By 2000, there were fewer than 200 people living on the streets of the City of Brotherly Love. That's in large part thanks to an extraordinarily well-run program, founded by Sister Mary and Joan McConnon. More than 95% of those who cycle through their Project H.O.M.E. (the acronym stands for Housing, Opportunities for Employment, Medical Care, Education) have never again returned to life on the streets — a success rate that has made the program a model for dozens of other U.S. cities. Meanwhile, Sister Mary, 55, has become the darling of luminaries like Bill Clinton, though that hasn't impacted her humility or her famously ribald sense of humor. When Jon Bon Jovi (a loyal Project supporter) described Mary to the press as a nun "who swears and spits," the good sister merely replied, "I do not spit" — and then returned to her work of tirelessly saving her city, one desperate citizen at a time.

Gilbert is the author of Eat, Pray, Love