This document discusses the challenges of partnering on major research platforms and facilities. It notes that the high costs and complexity of such projects have driven increased partnering between U.S. agencies and with international entities. However, ensuring alignment between partner processes and practices can be challenging. The document analyzes the practices of three science agencies - DOE, NASA, and NSF - to identify similarities and differences in their approaches to developing and managing large science projects. Understanding these comparative practices is important for facilitating effective interagency and international cooperation on major research infrastructure initiatives.