On June 14, 2016, for the first time in two centuries, an Atlantic salmon swam through the town of Howland, Maine bound for spawning grounds that had been inaccessible for generations. Along the riverbank, hundreds of people cheered as they helped celebrate the event marking the culmination of a remarkable seventeen-year effort by an unlikely and diverse alliance of people and organizations. From Mountains to the Sea tells the inside story of the Penobscot River Restoration Project drawing on interviews with more than fifty participants who helped navigate local politics and federal budgets and examines the challenges, compromises, and key turning points in the project to ultimately balance social and economy values and serve as a global model for large-scale ecosystem restoration.