Methods of assessing, for preliminary design purposes, the stiffness and capacity of pile foundations under seismic forces are presented. Although the main thrust of the paper is to aseismic design the methods are applicable to other forms of dynamic excitation of pile foundations. Emphasis is placed on expressions for pile stiffness and capacity in the form of simple formulae that can be incorporated into spreadsheet or similar types of software. The use of the equations is illustrated with a number of worked examples. Where possible the methods are justified by data from field testing of foundations at prototype scale.