Doppler broadening of annihilation radiation (DBAR) and positron annihilation lifetime spectroscopy (PALS) have been successfully applied to the study of positronium (Ps)-forming amorphous solids such as polymers and silicon oxide in the bulk. Implementing depth selectivity to DBAR and PALS by combining them with variable-energy positron beams considerably broadens their applicability. Variation of incident positron energy over a wide range enables depth-profiling, whereas tuning of the beam energy enables the studies of surfaces, interfaces and thin films. In this paper, we discuss fundamentals and applications of energy variable DBAR and PALS for Ps-forming polymers and silicon oxide. (C) 2008 Elsevier B. V. All rights reserved.