This paper presents an overview of the evolution, advancements, and capabilities of the temporal analysis of products (TAP) reactor system as a unique catalyst characterization tool. The origination of the TAP reactor based on molecular beam scattering experiments is briefly mentioned. The advancement in TAP reactor design from the TAP-1 system to the TAP-3 system is introduced to highlight its relevance as a Valuable tool for elucidating mechanistic and kinetic aspects of adsorption, diffusion. and reaction in gas-solid systems. Since the invention of the TAP reactor system, a series of TAP microreactor configurations has been introduced with different amounts of catalyst packing starting from the one-zone microreactor to the most recent introduction. the single particle microreactor in which a single Pt particle is packed among 100,000 inert quartz particles An advantage to decreasing the catalyst zone inside the microreactor is to eliminate non-uniformity in the active zone while still achieving high conversions (95%). Experimental designs and results coupling the TAP reactor to other experimental Systems Such as a time-of-flight mass spectrometer and atomic beam deposition system is also presented. Key results from recent TAP experiments are presented to show how the TAP reactor is used to answer fundamental questions in catalysis such as bridging the pressure gap between industrial catalysis and Surface science, understanding the surface lifetimes of reactive adspecies in TAP pump-probe experiments, finding kinetic rate constants related to changes in catalyst composition and its performance. (C) 2009 Elsevier B.V. All rights reserved