Mass customisation has been hailed as the manufacturing paradigm of the future, and has accordingly received much academic interest. Nevertheless, it is important to gain a better understanding of the ways in which mass customisation performance may be enhanced, in the light of the number of reported failures of mass customisation ventures. This thesis explores the use of collaboration in product development processes as a means of increasing mass customisation operational performance. The two collaborative partners of interest are suppliers and lead users – a specialised subset of users. The effects of lead users in the product development processes of mass customisation have not previously been evaluated, nor has their value been compared to that of suppliers. Accordingly, the aim of this study is to investigate the relative effects of collaborating with suppliers and lead users in the product development processes on mass customisation.