A topic of much current interest is the chemical reactivity in complex environments, involving dynamical processes spanning multiple scales in both time and space. While challenging to study using standard ensemble-averaged methods, it is amenable to investigations using single-molecule approaches. Ultimately, one would like to monitor the dynamics of individual molecules as they undergo chemical transformations through time-dependent spectroscopic studies, and to correlate various molecular properties with their immediate physical and chemical environments. This article provides an overview of the recent advances toward this goal and describes future developments and potential applications. (c) 2008 Elsevier B. V. All rights reserved.