Program DynaPile was developed to compute the dynamic stiffness of single piles or pile groups. The piles can be either floating piles or end-bearing piles. Vertical, horizontal and rocking dynamic stiffnesses will be generated by the program. The program will also generate the group reduction factors for pile groups under small excitation conditions. The method of computation is based on the consistent boundary-matrix method proposed by Blaney, Kausel and Roesset (1976).