An international consortium of botanic gardens and arboreta is launching a collaborative Ecological Restoration Alliance under the auspices of BGCI (Botanic Gardens Conservation International). We describe the Alliance and the ways in which it serves worldwide restoration efforts. Botanic gardens and arboreta are uniquely positioned to contribute to restoration science and practice. They have the plant collections and information required to understand flora and vegetation, and the horticultural expertise and experience needed to propagate, grow, manage, and conserve plants, all of which are essential for successful restoration. Botanic gardens work beyond their walls to network, educate, advocate, develop policy, build capacity, and engage in restoration projects throughout the world.