The Riesz theorem may refer to any of several mathematical theorems due to brothers Frigyes Riesz and Marcel Riesz:

• F. and M. Riesz theorem
• F. Riesz's theorem – Characterizes finite-dimensional Hausdorff topological vector spaces (TVSs).
• Riesz representation theorem
• M. Riesz extension theorem
• Riesz–Thorin theorem
• Riesz–Fischer theorem
• Riesz's lemma
• Riesz–Markov–Kakutani representation theorem