The European Solar Telescope (EST) is a pan-European project to build a next-generation 4-metre class solar telescope, to be located at the Roque de los Muchachos Observatory in the Canary Islands, Spain. It will use state-of-the-art instruments with high spatial and temporal resolution that can efficiently produce two-dimensional spectral information in order to study the Sun 's magnetic coupling between its deep photosphere and upper chromosphere. This will require diagnostics of the thermal, dynamic and magnetic properties of the plasma over many scale heights, by using multiple wavelength imaging, spectroscopy and spectropolarimetry.