DynaPile computes 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. 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). The dynamic model, which takes into account the whole soil medium in the analysis, can provide information about group-reduction factors of pile foundations if the soil properties are adjusted to account for the effective level of strains. Input parameters consist of the structural and dynamic properties of the pile, geometric configuration of the pile groups, soil properties, definition of excitation forces (in frequencies), and definition of superstructure masses.