The Dalgarno–Lewis technique [A. Dalgarno and J. T. Lewis, ‘‘The exact calculation of long‐range forces between atoms by perturbation theory,’’ Proc. R. Soc. London Ser. A233, 70–74 (1955)] provides an elegant method to obtain exact results for various orders in perturbation theory, while avoiding the infinite sums which arise in each order. In the present paper this technique, which perhaps has not been exploited as much as it could be, is first reviewed with attention to some of its not‐so‐straightforward details, and then six examples of the method are given using three different one‐dimensional bases.