Positron annihilation (PA) spectroscopy (PAS) is successfully used to study various types of defects in many kinds of materials. As experimental techniques become more precise and sophisticated, finer details about studied defects/materials can be obtained and, consequently, requirements for the quality of the theoretical description of the positron annihilation process in a given material also increases. In this paper, a short review of recent developments in PA defect studies is given. In particular, several examples of defect studies in metallic, semiconducting and insulating systems are discussed. Finally, new perspectives and problems for the theoretical description of positron-defect interactions are outlined. A tight cooperation between experiment and theory in PA studies is pointed out. (C) 2002 Elsevier Science B.V. All rights reserved.