Prototyping, the practice of building low-fidelity representations of products, services, or experiences in order to learn and test before proceeding, is at the heart of the human-centered design process. This paper, authored by a multidisciplinary group of museum practitioners, considers how and when to use the practice of prototyping for a variety of applications. We offer case studies and best practices around digital, experiential, and process-based prototypes from the J. Paul Getty Museum in Los Angeles, California, and the Queensland Museum in Brisbane, Australia.