“Now I have been invited to join enough different boards that I’ve learned how to say no, or recognize the hook when it’s in front of my nose,” says Adams, a Harvard Business School graduate who is currently a senior counselor at New York-based P.R. firm Burston-Marsteller. Adams says she currently sits on “six or seven” boards, but is now more selective about which ones she agrees to serve on, pursuing opportunities that fall within philanthropic areas she has defined for herself.

Some execs rely on recommendations from colleagues or mentors to decide which boards to join.

Scott L. Bok, co-chief executive of Greenhill, a Manhattan investment bank, worked at the law firm Wachtell, Lipton, Rosen & Katz earlier in his career, and after leaving, stayed in touch with Martin Lipton, one of the firm’s founding partners. When Lipton invited Bok in 1997 to join the board of Prep for Prep, a New York-based nonprofit that places minority students in independent schools, Bok said yes.

“He knew I’d been a supporter of the organization,” says Bok. “In choosing which nonprofits to work with, a lot of businesspeople take cues from their career mentors. That’s what I did.”

Sometimes the matchmaker between board and executive is not a work associate or mentor but a third-party board-matching service like BoardAssist or the United Way’s board-placement program, Linkages. These services present executives with information about nonprofits with open board seats and give them the opportunity to meet executive directors there. They also give executives information about what kinds of commitments each board requires, in terms of both money and time.

BoardAssist, which works with hundreds of nonprofits and makes 100 matches a year, arranged a match several years ago between George Mattson, a managing director at Goldman Sachs in Manhattan, and Volunteers of America, a national human-services nonprofit. Mattson hadn’t explored board service before he got the call from BoardAssist about V.O.A., but it coincided with Mattson, in his words, “feeling successful enough to look around a bit, and wanting to help people who haven’t been as fortunate.” In addition to the good timing, V.O.A. was a good fit for Mattson, who says “it felt very much like a hands-on, working board, meaning it was a lot about trying to manage and grow a big, complex organization, and a little less about benefits, dinners, and fundraising.”

Organizations like BoardAssist can help mediate between charities looking for a board member and potential candidates, many of whom have little time to spend vetting multiple boards, but are also loathe to waste time later on boards that don’t fit with their charitable goals and philosophies.

“It takes time, a lot of time” to find the right organizations and then to carry out a board member’s responsibilities, says Robert Levitan, co-founder of iVillage, an online community for women, and the co-founder and C.E.O. of Pando Networks, a peer-to-peer media delivery company. Levitan serves on three boards—New York Cares, whose board he joined with a friend; the Executive Council of New York, with whom he had worked on a project and was subsequently asked to join as a board member; and conservation group Rainforest2Reef, which was founded by a friend—and estimates he spends at least an hour a week on board-related activities, including attending meetings, reading materials, calling connections, and asking friends to contribute.

But he says it’s all worth it. “I feel blessed and fortunate to have everything I have in my life, and I was brought up with a sense of obligation to give something back,” Levitan says. “And it keeps me connected to things that matter on different level from my day-to-day business.”