The errors between thermoluminescence dates and archaeological dates obtained in an earlier series of 5 test programs are given. The present paper discusses known sources of error when thermoluminescent dates are derived from laboratory data. A method is given for compounding random and systematic errors in age, both for individual sherds and for the weighted average of a number of sherds from the same context. It is proposed that two error limits should be quoted for the date of a context: first, the standard error of the mean value as calculated from the experimentally observed root-mean-square deviation of the individual samples, and secondly, the expected overall error from the sources discussed in the paper. The former does not take account of systematic errors and is useful, therefore, only when comparing different contexts in the same site or locality where environmental conditions affecting the laboratory data are constant; the latter is more realistic for comparison of thermoluminescence dates with radiocarbon or archaeological chronology.