In 1993 the United States and Russia signed an historic agreement committing both countries to a broad range of cooperative activities in space. This agreement included the “development of a common space suit.” This paper describes the major elements of a Common Space suit System (CSS) approach, presents the current status of flight planning towards implementing the agreement, and discusses some future challenges.Planning the CSS program revealed different theoretical “levels of commonality,” ranging from minimum interoperability to a concept of a single, common design embodying common manufacturing and full interchangeability. Reviewing these reveals some of the practical limitations to commonality that relate to both evolution (of existing U.S. and Russian space suits) and revolution (a brand new space suit).This paper also takes an initial look at options for expanding interoperability between the EMU and Orlan-M, which are the two baseline EVA space suit systems for International Space Station (ISS). These interoperability issues arise from differences between the two EVA space suit systems. While potentially involving modifications to both country's EVA systems, incorporating these options would add robustness to the overall ISS EVA capability.