An overview of offshore wind turbine (OWT) foundations is presented, focusing primarily on the monopile foundation. The uncertainty in offshore soil conditions as well as random wind and wave loading is currently treated with a deterministic design procedure, though some standards allow engineers to use a probability-based approach. Laterally loaded monopile foundations are typically designed using the American Petroleum Institute p-y method, which is problematic for large OWT pile diameters. Probabilistic methods are used to examine the reliability of OWT pile foundations under serviceability limit states using Euler–Bernoulli beam elements in a two-dimensional pile–spring model, non-linear with respect to the soil springs. The effects of soil property variation, pile design parameters, loading and large diameters on OWT pile reliability are presented. Copyright © 2014 John Wiley & Sons, Ltd.