WinXAS is a new X-ray absorption spectroscopy (XAS) data-analysis program that runs under MS-Windows 95/NT. It offers a user-friendly graphical interface, supports various data formats, and includes advanced numerical algorithms beyond conventional XAS analysis. It provides an interface to the ab-initio theoretical code FEFF and is particularly useful for online data examination at synchrotron radiation facilities and for analyzing multiple-scan data, such as those from time-resolved experiments. WinXAS allows the processing of up to four data files simultaneously, with results that can be superimposed and compared. It also provides a graphical visualization of results and intermediate steps during data reduction. The program includes numerical subroutines for integrals, derivatives, Fourier transformations, and least-squares refinement. It supports conventional XAS data analysis, including background subtraction, $ E_0 $ determination, atomic absorption $ \mu_0 $, and fast Fourier transform. It also allows for XAFS refinements in k-space or R-space, and can use experimental or theoretical phases and amplitudes for single-scattering plane-wave XAFS refinements. WinXAS includes a FEFF interface, enabling users to perform XAFS analysis using FEFF-generated theoretical phases and amplitudes. It also supports energy-dispersive XAS data analysis, including energy calibration. WinXAS can handle large data sets from time-resolved experiments through macros, allowing for efficient data treatment. It also supports RasMol for molecular structure visualization. WinXAS is a versatile tool for XAS data analysis, offering a wide range of features for both educational and research purposes.WinXAS is a new X-ray absorption spectroscopy (XAS) data-analysis program that runs under MS-Windows 95/NT. It offers a user-friendly graphical interface, supports various data formats, and includes advanced numerical algorithms beyond conventional XAS analysis. It provides an interface to the ab-initio theoretical code FEFF and is particularly useful for online data examination at synchrotron radiation facilities and for analyzing multiple-scan data, such as those from time-resolved experiments. WinXAS allows the processing of up to four data files simultaneously, with results that can be superimposed and compared. It also provides a graphical visualization of results and intermediate steps during data reduction. The program includes numerical subroutines for integrals, derivatives, Fourier transformations, and least-squares refinement. It supports conventional XAS data analysis, including background subtraction, $ E_0 $ determination, atomic absorption $ \mu_0 $, and fast Fourier transform. It also allows for XAFS refinements in k-space or R-space, and can use experimental or theoretical phases and amplitudes for single-scattering plane-wave XAFS refinements. WinXAS includes a FEFF interface, enabling users to perform XAFS analysis using FEFF-generated theoretical phases and amplitudes. It also supports energy-dispersive XAS data analysis, including energy calibration. WinXAS can handle large data sets from time-resolved experiments through macros, allowing for efficient data treatment. It also supports RasMol for molecular structure visualization. WinXAS is a versatile tool for XAS data analysis, offering a wide range of features for both educational and research purposes.