The effects of pile spacing, number of piles, and configuration on displacement and bending response of pile groups in clay under dynamic lateral loading were investigated. The displacement response of pile group in clay is strongly nonlinear. Pile-soil-pile interaction is predominant for the groups with closer spacing and with greater number of piles. Group interaction causes reduction in the group stiffness and increase in damping of the pile group. Strong group interaction leads to significant differences in bending profiles of different row piles of the groups. Dynamic lateral loading increases the maximum bending moment and active pile length. Copyright © A. S. Elnashai and N. N. Ambraseys.