This dissertation in industrial design focuses on the gap between the context of design and the context of use. It aims to open up design to the layperson and investigate an active role for the layperson in the design of everyday products. Over the last century, the industrial paradigm has institutionalised and professionalised many practices, including product design. A binary spectrum of production and consumption has been established with distinct roles for the professional designer, who engages in production, and the consumer, who engages in consumption. However, this clear distinction has been blurred recently and the consumer, or layperson, is no longer involved only in consumption, but also in production. In this research I have explored and examined the participation of the layperson, or the non-professional, in design, which I refer to as lay design. It constitutes a shift for the professional designer from knowing what a future user would like to have towards knowing what a layperson would like to design, which is for most designers an unfamiliar way of thinking. I specifically investigated how the layperson can be involved in design through the use of so-called digital-physical toolkits, software applications where one designs in a digital environment and which outputs a physical product. Lay design is enabled by two developments: On the one hand, the creation of variable designs is enabled by computational design, and on the other hand, the fabrication of variable products is enabled by 3D printing. The two main questions that I focused on are: How will the roles of the professional designer and the layperson change when the latter engages in the design of personal products and how can designers develop digital-physical toolkits for the layperson to collaboratively create value and meaning? The theory that I drew on consists of existing approaches which involve the layperson in design, such as mass customisation, meta-design, and co-design, and I used the theory of technological mediation to analyse and discuss the mediating role of toolkits in lay design. I investigated the research questions through a series of studies, both analytical and experimental. For the experiments I took a constructive design research approach, which means that I engaged in the making of toolkit and product prototypes in order to obtain insights and an understanding of the subject. The main contribution of this research is a framework of lay design that consists of a set of principles and guidelines that enables the professional designer to develop digital-physical toolkits that empower the layperson to engage in the design of everyday products. Through the participation of the layperson in the design process, lay design constitutes value created by both the professional and lay designer, thereby eliminating the separation of production and consumption. The framework’s principles outline the basic ideas of lay design while the guidelines support the professional designer in the development of toolkits and their products in practice. Lay design is concerned with the layperson designing personal products and is therefore primarily self-serving. It deals with creating meaningful products by enabling the layperson to personify designs, meaning that the designed product cannot exist without its originator. This research established an understanding of design spaces and toolkits and of the roles the professional designer, layperson, and toolkits play. The implications of lay design concern the role of the professional designer, the way value is created, a shared accountability, and also the way designers are educated regarding the tool-sets, skill-sets, mindset, and knowledge.