Digital technologies have taken individualized advertising to an unprecedented level. But the convenience and efficiency of such highly tailored content comes at a high price: unbridled access to our personal data. The rise of sophisticated data-driven practices, otherwise known as “Big Data,” enables large datasets to be analyzed in ways that reveal useful patterns about human behavior. Thanks to these novel analytical techniques, businesses can cater to individual consumer needs better than ever before. Yet the opportunities presented by Big Data pose new ethical challenges. Significant scholarly research has examined algorithmic discrimination and consumer manipulation, as well as the ways that data-driven practices undermine our democratic system by dramatically altering the news ecosystem. Current scholarship has especially focused on the ways illegitimate foreign and domestic operatives exploit the advertising tools of digital platforms to spread fake and divisive messages to those most susceptible to influence. However, more scholarly attention should be devoted to how these digital technologies are exploited by legitimate political actors, such as politicians and campaigns, to win elections. By combining data-driven voter research with personalized advertising, political actors engage in political microtargeting, directing communications at niche audiences. Political microtargeting fits within a broader conversation about data-privacy regulation, as individuals lack sufficient control over how digital companies handle their personal data. The First Amendment currently limits data-privacy reform, so any meaningful changes must reconcile data privacy with the First Amendment. Professor Jack Balkin has argued that online service providers should be defined as “information fiduciaries,” or businesses that, because of their relationship with another, have taken on special duties with respect to the information they obtain in the course of the relationship. Because online service providers receive sensitive information from their end users, Professor Balkin argues they should be subject to additional regulation. Treating online service providers as information fiduciaries provides a viable means to reconcile the First Amendment with data-privacy regulation: the First Amendment has not prevented the state or federal government from regulating how certain professionals, such as doctors and lawyers, interact with their clients and use their personal information because these professionals share a fiduciary relationship with their clients. Therefore, consistent with the First Amendment, the government should also be able to subject online service providers to reasonable restrictions on their handling of end-user data. This Note expands Professor Balkin’s information-fiduciary framework by arguing that federal legislation should place fiduciary duties on online service providers. In doing so, it responds to scholarly critiques of Professor Balkin’s theory, particularly the criticism that he failed to show how information fiduciaries might function in practice. Using political microtargeting on Facebook as an example, this Note spells out the ways that fiduciary duties might be enforced. This Note argues that holding Facebook and other digital platforms that engage in political advertising to an information-fiduciary standard would ameliorate some of the adverse effects of political microtargeting and promote electoral integrity in the digital age.