This document is a working paper that examines the interaction between paid search advertising and display advertising. It aims to address whether display ads influence paid search and vice versa, the size of these effects, and their dynamic patterns over time. The paper also discusses the implications for online marketing metrics and optimal budget allocation when accounting for attribution of effects between the different channels and their dynamics. It was written by Pavel Kireyev, Koen Pauwels, and Sunil Gupta, with the goal of better understanding how attribution and dynamics impact the effectiveness of online advertising.