In this paper, we describe the recent progress which has been made in understanding the physics of electron transfer between conjugated polymers and semiconductor nanocrystals. Photoluminescence efficiency measurements and photoinduced absorption experiments are used to study the electron transfer and recombination processes. We also perform electrical measurements on thin films of nanocrystals in order to study the electron transport processes which are important in photovoltaic devices based on polymer/nanocrystal composites. (C) 2001 Elsevier Science B.V. All rights reserved.