An integrated Monte Carlo-Library Least-Squares (MCLLS) System has been developed and implemented to model the complete spectral response of energy-dispersive X-ray fluorescence (EDXRF) spectrometers and perform an inverse elemental analysis by an iterated Library LeastSquares method when an initial guess is provided. This software is a visualization system developed on the Borland C++ Builder platform and has a user-friendly interface to accomplish all qualitative and quantitative tasks easily. The software enables users to run the forward Monte Carlo simulation (if necessary) or use previously obtained Monte Carlo results that include differential operators and complete the sample composition inverse analysis just by selecting several modes of operation and providing simple inputs. An overview of the software is illustrated with experimental results on standard reference materials.