The theory and the case studies concerning the application of strategic models for the effectiveness of organisations usually refer to organisations of a large size. The aim of this Dissertation is to test the hypothesis that formal strategic models and concepts are or are not relevant to the development of small and medium size enterprises. Formal strategic models are formalised approaches to planning in other words tools for analysis as they have been developed by the management thinkers and authors of the last thirty years. For the purpose of providing the empirical evidence three organisations from three different sectors have been chosen. The first, IMPECO SA, is a commercial enterprise. The second, SOLID SA, is an advertising agency and the third, JUPE LTD, is a small manufacturing company.