The potential benefits of applying reactive distillation (RD) processes are taxed by significant complexities in process development and design. The design problem is formulated in the wider context of process development and engineering. From that perspective design methods for RD units developed over the last decades are classified and described. A fingerprint of the most representative work in the three categories, graphical, optimisation- and heuristic-based, is presented and deficiencies are identified. In response to a need for a more integrated design methodology, a conceptual model is offered which uses a hierarchy of embedded design spaces of increasing refinement and conjugates the strengths of both the graphical- and optimisation-based methods. (C) 2004 Elsevier Ltd. All rights reserved.