This annual review of X-ray fluorescence covers developments over the period 1999–2000 in instrumentation and detectors, matrix correction and spectrum analysis software, X-ray optics and microfluorescence, synchrotron XRF, TXRF, portable XRF and on-line applications as assessed from the published literature. The review also includes a survey of applications, covering sample preparation, geological, environmental, archaeological, forensic, biological, clinical, thin films, chemical state and speciation studies. During the current review period, further advances have taken place in the development of high resolution semiconductor detectors and in the design and application of XRF instrumentation for space and planetary research. Overall, the papers reviewed here again confirm the important contribution the XRF technique makes to a wide range of scientific endeavour.