A database containing information on over 35,000 coins from sites in southern Britain was established. This was used to investigate chronological and geographical distributions of fourth century Roman coinage in Britain, and the role of coins in archaeological dating. The regularity of finds supports a view of official supply policy as the principal determinant of the coins used, deposited and subsequently recovered. Throughout the fourth century, Britain received supplies of bronze from up to three mints of which one was always the primary source. One or two secondary sources supplemented this, particularly at times of major new issues. The few finds from other mints represent material that arrived through circulation and exchange. The only clear geographical variation Was after 388AD when new issues failed to circulate extensively beyond the towns. Variations between sites are related to differences in coin using and depositing practices. Three groups of sites were recognised: towns and larger settlements, villas and rural buildings, and temples. Differences between these are most apparent after 350AD when circulation and use underwent significant changes in the rural areas. Typical excavations of rural buildings produce few coins, probably representing accidental losses. On some sites casual loss accounts for only a small proportion of the recovered material. Here, votive deposition, rubbish disposal and non-recovery of hoards are the major sources of finds. A study of the stratified material reinforces the need for caution in using coins for dating, and has important implications for the use of coins in archaeological dating. Residuality and lengthy circulation severely limit inferences about the dates of deposition of the contexts in which coins are found. Throughout the fourth century, and probably also earlier, most coins were deposited within a few decades of their issue. Unfortunately for the archaeologist in search of a date for a deposit, examples of primary deposition are greatly outnumbered by residual and re-deposited material.