In mathematics, gap theorem may refer to:

• The Weierstrass gap theorem in algebraic geometry
• The Ostrowski–Hadamard gap theorem on lacunary functions
• The Fabry gap theorem on lacunary functions
• The gap theorem of Fourier analysis, a statement about the vanishing of discrete Fourier coefficients for functions that are identically zero on an interval shorter than 2π
• The gap theorem in computational complexity theory
• Saharon Shelah's Main Gap Theorem which solved Morley's problem in model theory