Of the 34 islands in Boston Harbor, Thompson Island is the closest to the city and, at 170 acres, one of the largest. The island has a variety of upland, wetland, and maritime communities, including forests; coastal shrublands; old fields; eroding bluffs; beachfront plant associations; freshwater wetlands; and the largest salt marsh (50 acres) among the Harbor Islands. Our walk around the island introduces us to the island's native and exotic plants, with particular attention to its freshwater wetland and salt marsh communities. Look for unusual, exotic maritime species, such as Lepidium latifolium and Senecio jacobea, which present issues for managing the island's habitats. The island also has interesting bird life, and binoculars are recommended. Bring lunch, water, and footgear that can get wet.