This chapter discusses the practical experience of obtaining user participation in the development and design process by focusing on the use of mock-ups within the project environment. It suggests that 'the cornerstone of minimising resistance to a new technology is user participation in the development and implementation process'. The chapter focuses on the benefits and challenges of using mock-ups within a design context, including a short discussion of some of the commercial implications. It also focuses primarily on projects that are concerned with the design and development of hardware. The chapter explores and explains the relevant factors that influence the successful use of mock-ups from both of these perspectives. It demonstrates that, because mock-ups are tangible, three-dimensional, realistic and understandable, when used appropriately they can provide a cost-effective and efficient method to involve end users in the design process and gain valuable design information. The chapter provides a number of case studies to demonstrate the practical use of mock-ups.