Online advertising is now the dominant form of advertising in many OECD countries, and offers businesses the ability to reach consumers in ways that could only have been imagined previously. Online advertising has the potential to benefit consumers through more relevant and timely advertising, and by funding a host of “free” online services. However, it also raises some new and complex challenges for consumers and consumer protection authorities. This report by the OECD’s Committee on Consumer Policy provides an introduction to the complex landscape that is online advertising. It outlines the potential benefits and risks for consumers, drawing on the behavioural insights literature where relevant.