EN
The interpolation properties of Cesàro sequence and function spaces are investigated. It is shown that $Ces_{p}(I)$ is an interpolation space between $Ces_{p₀}(I)$ and $Ces_{p₁}(I)$ for 1 < p₀ < p₁ ≤ ∞ and 1/p = (1 - θ)/p₀ + θ/p₁ with 0 < θ < 1, where I = [0,∞) or [0,1]. The same result is true for Cesàro sequence spaces. On the other hand, $Ces_{p}[0,1]$ is not an interpolation space between Ces₁[0,1] and $Ces_{∞}[0,1]$.