The Win-Tensor program is an interactive software for brittle faults and fractures kinematic analysis and tectonic stress determination from geological and earthquake focal mechanisms data in structural geology, neotectonic and seismotectonic investigations. Besides its capacities for data storage and management, it has been designed for reconstructing the four parameters of the reduced paleostress - or stress - tensor (orientation of the three principal stress axes and the shape ratio of the stress ellipsoid) using a refined Right Dihedron method and an iterative Rotational Optimisation procedure. It allows kinematic separation of fault-slip and focal mechanism data together with progressive stress tensor optimisation. Emphasis is given to user interactivity for controlled data acquisition, data selection and rotation, tensor estimation and optimisation, graphical representation and quality ranking according to the World Stress Map data base. Win-Tensor is the Windows version of the Tensor program developed originally in Quick Basic for DOS. Development of the DOS version started in 1990 with the aim of testing the different code available at that time for handling brittle structural data, consigning them in a structured data base and performing paleostress reconstruction. It rapidly evolved into a user friendly program and was adopted by an increasing number of researchers which provided their feedback and suggested many improvements. This program, which is a by-product of the author’s personal research, has been developed in order to meet the needs of field geologists active in brittle fault analysis and paleostress reconstructions, an emerging standard method in structural geology. Conversion of the Tensor program into Win_Tensor written in Visual Basic 6.0 started in 2001 and was almost finished by late 2010. It was then continuously upgraded and further developed until now. It is designed using the same structure and user-friendly approach that were appreciated with the Dos version. Win_Tensor is not simply an upgrade of the Dos version in to the Windows technology but brings also important developments of the original concept. The Win-Tensor program is freely available for academic and scientific purposes. It is widely distributed work wide and benefitted from the feedback from the users. It has been used in numerous academic thesis and published papers in peered –reviewed journals. It is now widely recognized as a classical method in structural geology. Tensor program is available from the author, by request at the Contact address or by download from his web site. It is provided freely for academic and scientific use only. It cannot be sold, transmitted or used by private companies prior to written agreement from Dr. D. Delvaux. In the case of publication of results obtained by this program, it is requested to mention the origin of the program by citing the following reference article: DELVAUX, D. AND SPERNER, B. (2003). Stress tensor inversion from fault kinematic indicators and focal mechanism data: the TENSOR program. In: New Insights into Structural Interpretation and Modelling (D. Nieuwland Ed.). Geological Society, London, Special Publications, 212: 75-100. Tensor Web site: http://http://www.damiendelvaux.be/Tensor/tensor-index.html