Curvatures are the central concept in geometry. The notion of curvature introduced by B. Riemann faithfully reveals the local geometric properties of a Riemann metric. This curvature is called the Riemann curvature in Riemannian geometry. The Riemann curvature can be extended to Finsler metrics as well as the sectional curvature. In this chapter, we will give a local formula for the Riemann curvature of a Randers metric. Then we shall also study the relationship between the flag curvature and some non-Riemannian geometric quantities.