Over the last two decades an extensive body of evidence has accumulated on the validity of measures of life evaluation and affect. This evidence strongly supports the view that measures of both life evaluation and affect capture valid information. This does not mean that these measures are universally valid or devoid of limitations. However, these limitations do not suggest that measures of subjective well-being should be regarded as not fit for purpose if used with appropriate caveats. The evidence base for eudaimonic measures is less clear. While psychologists have studied concepts related to eudaimonic well-being such as good psychological functioning for some time, it has proved more difficult to pull together a summary of the literature addressing validity in the terms set out above. This does not mean that eudaimonic measures are not valid, but suggests that further work is needed before a definitive position can be taken on the validity of these measures. Table 1.2 provides a summary of the evidence for the validity of subjective well-being outlined above.