Landmarks carries out its mission through a number of events and activities. The organization conducts architectural and cultural surveys of neighborhoods and buildings in St. Louis. This research often leads to nominations of these sites or districts for inclusion on the National Register or designation as local historic districts or city landmarks. Landmarks also engages in a number of educational activities geared toward various segments of the community. The organization's bimonthly newsletter keeps its membership and the broader public informed about preservation issues in St. Louis.
Landmarks also distributes information through other publications.
Each year, the organization releases St. Louis' Eleven Most Endangered Sites to call attention to the City's most threatened landmarks. More recently, Landmarks has added St. Louis' Eleven Most Enhanced Sites to honor noteworthy preservation efforts. The potential for preservation and restoration of historic structures in St. Louis is better now than it has been at any time in the past decade. In the early 1980s, the City of St. Louis led the nation in historic rehab. The 1986 federal tax act reduced the tax incentives that had made many of those projects economically viable, and historic rehab activity supported by tax credits in the City declined by 96 percent.