Advertisers have long striven to design ads that elicit emotion in viewers but have struggled to measure the extent to which they have been successful. This chapter illustrates how new technology for measuring emotional responses has been applied to evaluating digital advertising effectiveness. It presents future directions for this research and suggests how new research methods might be used to programmatically deliver content based on emotional reactions in addition to being used for pre- and/or post-testing of advertisements. Cognitive responses to advertisements can be captured quite effectively via surveys. However, one caveat in considering the strength of findings related to emotion is that most of the measures have also been obtained from self-report questionnaires involving post-hoc cognitive reflection. Post-hoc reporting of an earlier emotion can be influenced by the end-state emotion as well as by a person's ability to map remembered, possibly complex, feelings to the various choices on the questionnaire, which tend to be simple descriptors.