The chapter considers consumer input in the 3D printing environment in light of 3D models designed for mass customisation. Focusing on the nature of this collaborative process, the chapter highlights issues in relation to copyright authorship and ownership as they relate to the product designer and consumer. Pointing to the blurring of the line between designers and consumers in terms of their role in the design process, the chapter firstly demystifies terminology leading to mass customisation for 3D printing, before moving to a consideration of the elements of protection arising from the design document—at the time of design (by the product designer), as well as at the time of customisation (by the consumer). In particular, the chapter focuses on the scope of protection of mass customisation, with the emphasis on copyright classification and originality. Thereafter, it discusses the role of consumers as co-producers—or prosumers—of designs and analyses their legal status in copyright law. Through the application of recent UK and EU case law, the chapter demonstrates the manner in which both product designers and consumers may have a claim to their rights of ownership and authorship of customised 3D models. In bringing the chapter to a conclusion, the authors recommend a short-term solution based on licensing but emphasise the need for a policy change to address the void left in the existing copyright framework as it relates to mass customisation of 3D printing.