This text is a bridge across what sometimes seems a divide between hard and soft OR/MS. It demonstrates that the views which are often characterized as hard and soft OR/MS are not really in opposition to one another but are addressing different types of issue. It explores the development and use of explicit models in management science. It discusses the way in which models are built and the way in which they should be used. The emphasis is on modelling rather than mathematics, though some familiarity with algebra and statistical ideas will be expected of the reader. It is careful to pace management science within a framework which is defensible in the face of attacks on rational methods in business. It argues for their relevance alongside other aspects of management such as intuition, vision and leadership.