The Python programming language has emerged as the “Language of GIS”, providing a powerful geospatial and scientific development environment whilst also being ideal for rapid prototyping and a good introductory language for first-time programmers. The open source environment is strategically important to the Met Office as we strive to meet the increasing need to collaborate freely and openly in academic and commercial partnerships. The Met Office employs a team of software engineers to develop, simplify and improve its scientific capabilities by contributing to the the open source community. The focus of much of this effort has been on two new open source packages. Cartopy [1] is a new mapping library that builds on Python’s matplotlib module. Cartopy exposes an intuitive interface for the transformation and visualisation of geospatial vector and raster data. Iris [2], implements a generalised n-dimensional gridded data model to isolate analysis and visualisation code from file format specifics. The Iris data model is a result of close collaboration with the CF Data Model community. In addition to common GIS file formats, it also has read/write support for a variety of scientific file formats including NetCDF. This talk will give details of the Met Office's involvement in the open source community, including demonstrations of Iris and Cartopy and outline areas of future development. [1] - http://scitools.org.uk/cartopy/docs/latest/ [2] - http://scitools.org.uk/iris/docs/latest/