Abstract. We give estimates for the approximation numbers of composition operators on H 2 , in terms of some modulus of continuity. For symbols whose image is contained in a polygon, we get that these approximation numbers are dominated by e −c √ n . When the symbol is continuous on the closed unit disk and has a domain touching the boundary non-tangentially at a finite number of points, with a good behavior at the boundary around those points, we can improve this upper estimate. A lower estimate is given when this symbol has a good radial behavior at some point.As an application we get that, for the cusp map, the approximation numbers are equivalent, up to constants, to e −cn/ log n , very near to the minimal value e −cn . We also see the limitations of our methods. To finish, we improve a result of El-Fallah, Kellay, Shabankhah and Youssfi, in showing that for every compact set K of the unit circle T with Lebesgue measure 0, there exists a compact composition operator C φ : H 2 → H 2 , which is in all Schatten classes, and such that φ = 1 on K and |φ| < 1 outside K.