Jupyter Notebooks are code-centric documents including prose, maths, code, and rich output, such as images and HTML. These are all stored in a structured JSON file, with metadata about each input and output. nbconvert is a highly extensible tool for converting those JSON notebooks to other formats, such as HTML, LaTeX, PDF, and restructuredText. nbconvert powers the web service nbviewer, which renders any notebooks on the Web as HTML, so that they can be read by anyone with a browser and internet connection. We will cover the various ways you can extend nbconvert, from defining your own export formats to customising the output with Jinja templates, enabling things like hiding input or boilerplate cells.