According to some authors development of monolithic catalysts and/or reactors has been one of major achievements in the field of heterogeneous catalysis and chemical reaction engineering of the recent years. This work is aimed at pointing out the advantages of monolithic catalysts and/or reactors with respect to the conventional ones, with particular focus on the integral approach to the catalyst and reactor design. The paper is divided into several parts. The first part gives basic definitions and classification of monolithic catalysts, including basic features of the monoliths and factors that have proceeded to the development and application of the monolith structures. It is explained that monoliths belong to the class of the catalytic reaction systems, where usual differences between catalysts and reactors, arising from their action level, are diminishing. Second part of paper is devoted to the preparation of monolithic catalysts. Next part deals with their commercial application with particular emphasis on the less known applications, and those which are still under development. The paper concludes with forecast of potential monoliths applications and ends up with the future research priorities and directions. (C) 2006 Elsevier B.V. All rights reserved.