In the last few decades, there has been growing concern about climate change and, consequently, the need to be more sustainable with our environment. The transition to a more sustainable design and manufacturing system is urgent, with the role of the industrial design engineer being crucial in driving this change, as design can condition up to an 80% of the environmental impact of a product. On this basis, the concept of Circular Design (CD) arises. Born out of the need for a more fitting term for the philosophy promoted by sustainable design, eco-design and green design, CD may be the key to moving away from Linear Economy (LE) and enter Circular Economy (CE). This contribution aims to propose a theoretical approach to a CD definition. A systematic literature review (SLR) has been made to define CD and a literature review assessment has been carried out in order to analyse the state of art of CD research. Moreover, CD fundamentals are defined and several strategies, tools and guidelines for CD product development are discussed. Conclusions from the SLR and the literature review assessment are presented.