  In these lectures we provide a basic introduction into the topic of
dispersion relation and analyticity. The properties of 2-point functions are
discussed in some detail from the viewpoint of the K\"all\'en-Lehmann and
general dispersion relations. The Weinberg sum rules figure as an application.
The analytic structure of higher point functions in perturbation theory are
analysed through the Landau equations and the Cutkosky rules.
