Geostrategy, a subfield of geopolitics, is a type of foreign policy guided principally by geographical factors^{[page needed]} as they inform, constrain, or affect political and military planning. As with all strategies, geostrategy is concerned with matching means to ends. Strategy is as intertwined with geography as geography is with nationhood, or as Colin S. Gray and Geoffrey Sloan state it, "[geography is] the mother of strategy."

Geostrategists, as distinct from geopoliticians, approach geopolitics from a nationalist point of view. Geostrategies are relevant principally to the context in which they were devised: the strategist's nation, the historically rooted national impulses, the strength of the country's resources, the scope of the country's goals, the political geography of the time period, and the technological factors that affect military, political, economic, and cultural engagement. Geostrategy can function prescriptively, advocating foreign policy based on geographic and historical factors, analytically, describing how foreign policy is shaped by geography and history, or predictively, projecting a country's future foreign policy decisions and outcomes.

Many geostrategists are also geographers, specializing in subfields of geography, such as human geography, political geography, economic geography, cultural geography, military geography, and strategic geography. Geostrategy is most closely related to strategic geography.

Especially following World War II, some scholars divide geostrategy into two schools: the uniquely German organic state theory; and, the broader Anglo-American geostrategies.

Most definitions of geostrategy below emphasize the merger of strategic considerations with geopolitical factors. While geopolitics is ostensibly neutral — examining the geographic and political features of different regions, especially the impact of geography on politics — geostrategy involves comprehensive planning, assigning means for achieving national goals or securing assets of military or political significance.

The term "geo-strategy" was first used by Frederick L. Schuman in his 1942 article "Let Us Learn Our Geopolitics." It was a translation of the German term "Wehrgeopolitik" as used by German geostrategist Karl Haushofer. Previous translations had been attempted, such as "defense-geopolitics". Robert Strausz-Hupé had coined and popularized "war geopolitics" as another alternate translation.

[G]eostrategy is about the exercise of power over particularly critical spaces on the Earth's surface; about crafting a political presence over the international system. It is aimed at enhancing one's security and prosperity; about making the international system more prosperous; about shaping rather than being shaped. A geostrategy is about securing access to certain trade routes, strategic bottlenecks, rivers, islands and seas. It requires an extensive military presence, normally coterminous with the opening of overseas military stations and the building of warships capable of deep oceanic power projection. It also requires a network of alliances with other great powers who share one's aims or with smaller "lynchpin states" that are located in the regions one deems important.

— James Rogers and Luis Simón, "Think Again: European Geostrategy"