This document discusses 3D printing and its applications in medical libraries. It begins by explaining what 3D printing is and how it works. It then explores the various materials that can be 3D printed, including plastics, metals, electronics, proteins and living cells. Examples are given of how 3D printing is used for medical purposes such as surgical modeling, implants, prosthetics and transplants. The document also discusses emerging applications like bioprinting and 4D printing. It considers some of the challenges and opportunities 3D printing presents for medical libraries.