Steinitz's theorem may refer to any of the following results by German mathematician Ernst Steinitz (1871–1928):

• Steinitz's theorem on the graphs of three-dimensional convex polyhedra
• Steinitz exchange lemma on bases of finite-dimensional vector spaces
• Lévy–Steinitz theorem on the convergence of rearranged infinite series of vectors
• Several variations of Carathéodory's theorem (convex hull) on the enclosure of points in the convex hulls of other points
• Steinitz's theorem (field theory) on simple extensions