Urchin (Universal Renderer, Creating Helpful Images for Neuroscience) is a free and open source tool for neuroscientists that supports interactive exploration of large-scale electrophysiology and imaging datasets. Urchin is only the renderer, to control Urchin and display brain regions you need to use the Python API which can be found on our website. Urchin currently supports the Allen CCF mouse atlas and the Waxholm rat atlas. As a community-driven project we hope you will report back about what you find useful and frustrating so that we can make changes in the future. Please use the issues page on Github for this purpose.