RAT (Radar Tools) is a small collection of tools for processing SAR (Synthetic Aperture Radar) remote sensing data, packed together in a nice graphical user interface. Our motivation to start the development of RAT is that modern remote sensing software like Erdas Image or ENVI include only some basic SAR functionality. Advanced algorithms in SAR polarimetry (PolSAR), interferometry (InSAR) and polarimetric interferometry (PolInSAR) have to be implemented by oneself. So we descided to start the development of RAT. RAT should bring modern SAR algorithms to a wider user-base by simplifying in particular the data handling and processing of complex SAR data. RAT is planned as an ongoing community effort, i.e. there will be no final version with a certain functionality. It is our idea to include more and more SAR tools in future and to make them freely available to the scientific community. We of course also hope for external contributions. Because of this, the programming interface of RAT is kept quite simple and adding own functions is quite easy. Function templates are included in the distribution and a step-by-step description of how to program a RAT module will appear soon in the documentation.