Although the number of firms adopting corporate volunteerism programs is rising steadily, very few firms are assessing the benefits of such programs on target groups, such as employees and nongovernmental organizations (NGOs), and identifying the conditions under which benefits to the various groups are maximized. This study addresses both by examining the conditions of employees’ corporate volunteer assignments that lead to increased employee engagement, sustainability of the volunteers’ project within the NGO, capability development for the business unit, and employees’ continuation of volunteerism. Using a longitudinal and multisource design, responses from 116 corporate volunteers from a global pharmaceutical organization are matched with responses from their NGO managers and their business unit managers at 3 points in time: at the start of the volunteer assignment, at the end of the assignment, and 6 months after the completion of the assignment. Across these outcomes, we found that employees’ volunteer assignments are most valuable when they are international, when the volunteers perceive that their projects contribute meaningfully the NGO's functioning, when volunteers have professional skills (and are able to use them), when there are opportunities for skills to be developed that can be applied in the volunteers’ regular work role, and when the NGOs have tangible resources to sustain the volunteers’ projects.