Nonprofits rely heavily on volunteers, but most CEOs do a poor job of managing them. As a result, more than one-third of those who volunteer one year do not donate their time the next year—at any nonprofit. That adds up to an estimated $38 billion in lost labor. To remedy this situation, nonprofit leaders must develop a more strategic approach to managing this overlooked and undervalued talent pool. The good news is that new waves of retiring baby boomers and energetic young people are ready to fill the gap.