Modern research software is the basis of scientific progress in geophysics by supporting data collection, data analysis, and numerical simulation. These codes span the range from small one-off scripts developed by individual researchers up to large packages with thousands of users. While there is increasing awareness about best programming practices, scientists are rarely prepared to scale their codes into team projects developed by  larger communities. However, growing a sustainable software project and the community of practice that surrounds it is a prerequisite to make scientific software development more efficient and research more reproducible.