Much of the daring work in Mary Ellen Mark's new book, Mary Ellen Mark: 25 Years (Bulfinch, $60), was made on assignment for magazines. That's surprising, given the timidity with which most of today's magazines use photography. But it's easy to understand when you consider the extraordinary compassion and artistry Mark brings to her often sensational subject matter. Whether she's photographing glue‑sniffing street urchins in the Sudan, state‑supported heroin addicts in London, or Indian circuses (a recent project to which she devotes a separate 26‑page section of the book), she never exploits the freakish nature of those subjects the way a lesser photographer might. That's something not lost on Mark's picture editors at Fortune, Rolling Stone, National Geographic, Texas Monthly, and the New York Times Magazine. They know that Mark will push beyond her subjects' lurid surfaces. "Access is crucial to the kind of work I do," she says. "But there's no secret to it. I just explain to people what I'm doing, and they make up their own minds about whether they want to let me in." Mark says the process has gotten a little easier over the 25 years of her career because she's become more sure of herself. "I think if you're confident about what you're doing, people can feel it," she says. But Mark never takes a subject's invitation ‑or for that matter, her own abilities‑ for granted. "When I start an assignment, I always feel that I'm going to fail," she says. "Ask any of my editors. I always call them and say, 'I'm desperate, I can't get it.' It's almost a neurotic thing that I have to go through. And then something will happen and I'll feel I'm getting somewhere. It's an almost physical feeling -almost athletic‑ when you realize you're finally on track." Clearly, photography is a highly emotional experience for Mark, and that may be the source of her empathy. "These people who live on the edges ... I'm touched by their passions," she says. "I want my pictures to say something about the lives of people who don't have the lucky breaks."