[Truncated abstract] The realization in 1999 that the authigenic phosphate, xenotime, could be used in geochronological studies to place age constraints on burial events that affected sedimentary basins has opened numerous opportunities for establishing timeframes for sedimentary basin analysis. Since then, the mineral has been used to place new and novel age constraints on diagenesis, metamorphism, and hydrothermal alteration and mineralization events. Whilst these studies were successful, they identified many complexities in xenotime growth and were restricted to specific areas or single basins: they do not convey, demonstrate or explore the immense variety of geological applications in which xenotime may provide unique geochronological constraints. This thesis explores the nature of authigenic xenotime, utilizing studies in three different Proterozoic sedimentary basins: two in Australia, southwestern Australia and the Northern Territory, and the third in the United States of America. The thesis includes a number of discrete studies demonstrating different aspects of xenotime growth, elucidated from detailed petrography, geochronology and geochemistry of authigenic xenotime. An integrated textural, geochemical and geochronological study of authigenic xenotime from the Mt Barren Group, SW Australia, establishes an absolute timescale on some of the many processes involved during the diagenesis of siliciclastic units. ... positions and trends and broadly confirm the chemical discrimination criteria established for an Archaean basin. However, the Proterozoic data are shifted to lower Gd-Dy values and extend beyond the original field outlines, causing more overlap between fields intended to discriminate xenotimes of different origin. The plots were revised to encompass the new data. This study has significantly extended our knowledge of the nature of authigenic xenotime. It was found that xenotime may form in (meta)sediments in response to a large number of post-depositional processes, including early- and latediagenesis, (multiple) basinal hydrothermal events and low-grade metamorphism. A combination of detailed petrography and in situ geochronology provides the best avenue to decipher complex growth histories in xenotime. With further development, it is likely that xenotime geochemistry will also prove diagnostic of origin and can be incorporated into the interpretation of age data. The number of potential applications for xenotime geochronology has been expanded by this study.