Dorothy Day took seriously Christ's command to be responsible for our neighbor. She was a fool for Christ's sake: her boss was the individual on the street who was forgotten by society, the one we see each day, the one on the park bench who smells of alcohol and urine. Young Marxist journalist in Chicago, she became a beacon to both the poorest of the poor and the Christian community: we are called by Christ to respond passionately, Day understood the urgency of His call. Inspired by an itinerant French philosopher and farmer named Peter Maurin, Day set up Houses of Hospitality to help feed, clothe, and comfort the poor - the very basis of Christianity, lived through the Beatitudes.
A good starting point to start exploring Dorothy Day's life is to read a brief biography. More in-depth information on Day can be found at the Dorothy Day Library on the Web. I have links to many more resources below as well. Do not pass up a chance to read her autobiography, explained below. Also, a recent (1996) movie portraying the life of Dorothy Day is Entertaining Angels - The Dorothy Day Story. It can be found at most all video rental stores; read a review of it as well. Be careful while you watch it, however - it does indeed portray Dorothy's missionary zeal, but neglects to make note of the profound spirituality that drove her work (and must drive ours!). This is perhaps a common problem with social justice viewed from a religious perspective.
(Photo Credits: Marquette U and Fellowship Magazine)