This paper presents the specificities of micro-structured reactors as compared to conventional fixed-bed reactors through two case studies devoted to (i) hydrogen production by methanol steam reforming, (ii) hydrogen purification by water-gas shift (WGS). Key features like catalyst coating stability. temperature and pressure management, effects of operating conditions (residence time, pressure drops, etc.) are well identified as controlling the micro-reactor performances for methanol reforming. These devices are also shown to be excellent tools for fast access to reaction kinetics as exemplified for the WGS reaction, Subject to operating conditions carefully chosen to ensure proper hydrodynamics, in order to use conventional plug flow reactor models for extracting rate constants. (C) 2006 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.