This report focuses on the development of a new method of analysis of laterally loaded piles embedded in a multi-layered soil deposit treated as a three-dimensional continuum. Assuming that soil behaves as a linear elastic material, the governing differential equations for the deflection of laterally loaded piles were obtained using energy principles and calculus of variations. The differential equations were solved using both the method of initial parameters and numerical techniques. Soil resistance, pile deflection, slope of the deflected pile, bending moment and shear force can be easily obtained at any depth along the entire pile length. The results of the analysis were in very good agreement with three-dimensional finite element analysis results. The analysis was further extended to account for soil nonlinearity. A few simple constitutive relationships that allow for modulus degradation with increasing strain were incorporated into the analysis. The interaction of piles in groups was also studied.