The Carpentries, an open source project that develops training and instructing resources for researchers, has developed a membership program that is key to our sustainability and mission. This program creates communities of open source practices at organisations around the world and supports the open materials and forums of The Carpentries. We have learned from our various successes and challenges, continue to assess the effectiveness of this program, and are preparing for the challenges of adapting this program to be effective in our rapidly growing and diversifying community.