To enable packaging machinery manufacturers to compete at all international level, it is necessary to introduce them to more advanced design methods and technologies. For years, the evolution of packaging machinery has relied heavily oil trial-and-error methods. The demands for continual increases in the performance capabilities of the machines, escalating legislation, environmental directives and changes in the characteristics of the product require rapid development of existing machine designs and the creation of new machines. This paper discusses the needs of SME packaging machinery manufacturers and identifies their requirements for methods in support of the design and redesign of packaging machinery. The need to identify, capture and manipulate design knowledge is critical for SMEs, where all too often design records are incomplete. Furthermore, a systems modelling approach that provides for support over the conceptual, embodiment and detailed design phases is essential for the rapid and effective development of designs. In order to meet these requirements, a methodology is proposed which incorporates 'constraint modelling' techniques. The methodology provides for experimental investigation and computer-based modelling, which together aid the designer in gaining a fundamental understanding of the design problem. This enables the identification and representation of design knowledge, the determination of the limitations of an existing design, the evaluation of alternative designs and redesign strategies, as well as the embodiment, refinement and optimization of design solutions. The theory of 'constraint modelling' is discussed and the various phases of the methodology described. The applications of the methodology to a new machine design and a redesign program are also detailed. Copyright (C) 2001 John Wiley Soils, Ltd.