This workshop provides the first opportunity for the UIST community to discuss sustainability challenges and opportunities in rapid prototyping. We will discuss key issues such as waste generation from intermediate prototypes, strategies for sustainable materials, circular prototyping (e.g., promoting re-use of components), knowledge sharing infrastructures (e.g., open-sourcing hardware), and so forth. The goal is to identify potential HCI research directions that can foster a more sustainable "making" environment inside of labs and beyond.