Problem Solving's focus is today's 85,000 alumni and how they are using their leadership and problem-solving skills to change the world for the better as corporate leaders, social entrepreneurs, nonprofit professionals, public servants, generous philanthropists, and good citizens quietly contributing to their communities. Its 200-plus brief stories are the book's primary vehicle for sharing alumni's experience. These stories can be thought of as mini case studies of the myriad ways that alumni are tackling education, health, environment, poverty, inequality, and a host of other challenges. They also highlight how social impact journeys evolve over a person's lifetime. The book is the culmination of research and development work conducted from 2015 through 2018 in collaboration with HBS alumni, students, faculty, and staff. Designed to be engaging and informative, the book can be explored in a variety of ways--through a cover-to-cover reading, by skipping to sections of special interest, or just hopscotching through, hopefully finding something of interest wherever the reader lands.--