KLEIN MATHEMATICA Package for Radar Polarimetry Based on Spinor and Tensor Algebra. The authors describe KLEIN, a Mathematica package, designed to be used as a support and verification tool for scientific calculations in radar polarimetry based on spinor and tensor algebra. KLEIN is written in Mathematica, version 4 (Wolfram, 1999) and comes with a complete documentation (file: kleindoc.ps) and the full source code (file: klein.m). In addition to this, an example notebook (file: kleindemo.nb) is provided to demonstrate the mode of operation for every major KLEIN module.