Abstract The determination of stiffness and damping of piles is an important step in the analysis of pile-supported structures subjected to dynamic loading.; The first part of this study examines the use of approximate methods to evaluate the impedance functions of single piles and pile groups. The group impedances derived from the superposition of the two-pile solution are compared with those obtained from direct analysis. Good agreement is observed for floating piles in homogeneous and nonhomogeneous soil profiles.