*** Xiao This Small Business Innovation Research (SBIR) Phase II project will develop a high performance microfocus x-ray fluorescence (MXRF) instrument for geochemical applications. X-ray fluorescence is an useful analytical tool that can perform nondestructive elemental analysis on essentially any sample with high sensitivity. A serious limitation to current commercial MXRF systems is a lack of X-ray intensity on the samples because only a small fraction of the X-rays from conventional sources can be captured using pinhole collimators or monocapillaries. Phase I results show that this MXRF instrument, designed around an innovative polycapillary focusing lens, can improve measurement sensitivity (10x), speed (100x), and spatial resolution (from 100 to 20 microns) of current commercial MXRF instruments. Phase II will develop a laboratory prototype instrument and a simplified system for field use, and performance will be tested using various geological samples. Performance will be compared to currently available MXRF systems and to electron microprobes to understand the advantages of the new instrument for geologists and other end-users in industry and science. A successful MXRF would significantly benefit geochemistry and various industries, including semiconductor manufacture, environmental remediation, and industrial plating. It will also find application in scientific instrument manufacture.