The observation that many models are built but few are used has almost become a commonplace in the management science and operations research literature. Nevertheless, the statement remains to a large extent true today, also and perhaps even more so where marketing models are concerned. This led Philippe Naert, now about four years ago, to write a concept text of a few hundred pages on the subject of how to build imple men table marketing models, that is, models that can and will be used. One of the readers of that early manuscript was Peter Leefiang. He made suggestions leading to a more consistent ordering of the material and pro posed the addition of some topics and the expansion of others to make the book more self-contained. This resulted in a co-authorship and a revised version, which was written by Peter Leefiang and consisted of a reshuffling and an expansion of the original material by about fifty per cent. Several meetings between the co-authors produced further refinements in the text and the sequence of chapters and sections, after which Philippe Naert again totally reworked the whole text. This led to a new expansion, again by fifty per cent, of the second iteration. The third iteration also required the inclusion of a great deal of new literature indicating that the field is making fast progress and that implementation has become a major concern to marketing model builders.
