This report reviews design principles and construction problems associated with pile foundations, and recommends criteria based on current knowlege. The problem of determining whether or not the site conditions are such that piles must be used is discussed, as well as the selection of the pile type. The ultimate load on a pile is the load that can cause failure of either the pile or the soil. The pile failure condition may govern design where pile points penetrate dense sand or rock, but in most situations, ultimate load is determined by the soil failure. The computation of the ultimate load is discussed. For design purposes the ultimate load is separated into two components: the base or point load, and the shaft or skin load. The displacements needed to mobilize skin resistance, the mechanics of load transfer between pile and soil, and the settlement analysis of pile foundations is reviewed. Pile spacing, lateral deflection, slope or pile axis, position and magnitude of maximum bending moment are covered, as well as lateral loading caused by horizontal displacement, buckling, and pile driving. In-situ full-scale pile load tests are also discussed.  The report for this topic can be purchased at https://www.trb.org/news/blurb_detail.asp?id=3511