Successful open data initiatives involve more than just putting datasets online. This research note draws on an exploration of a number of different open data projects around the world to highlight key building blocks that open data initiatives commonly involve.Open data initiatives can be led by governments proactively releasing data they hold, or they may be led by private actors or civil society who collate relevant public data in ways that make it more accessible. Initiatives can focus on a specific topic (e.g. environmental statistics, transport data or international aid flows) collating data from across multiple jurisdictions, or initiatives might be centered on a particular geographical area or institution, seeking to increase access to all the datasets relating to a particular region, state or government body.