Every day, billions of people around the world use the Internet to share ideas, conduct financial transactions, and keep in touch with family, friends, and colleagues. Users trust the Internet to send and store personal medical data, financial information, business communications, and even intimate conversations over this global network. Trust in the privacy and security of the Internet is enormously important to its success as a source of economic activity and an unparalleled tool for free expression. At the same time, recent data breaches, cybersecurity incidents, and controversies over the privacy of online services are heightening Americans’ awareness of online threats.We hypothesize that lower levels of trust in the privacy and security of the Internet, taken together with a range of other factors, are associated with reductions in online activity. Using data from the July 2015 Computer and Internet Use Supplement to the Current Population Survey, we aim to shed light on the relationship between online privacy and security concerns and a range of important Internet-based economic and civic activities. Questions in this survey included whether online households had experienced an online security breach during the year preceding the survey; whether they experienced online harassment; what concerned them the most when it comes to online privacy and security risks; and whether concerns about privacy or security stopped them from conducting financial transactions, buying goods or services, posting on social networks, or expressing a controversial opinion online.In this study, we employ quantitative analysis to assess a link between indicators of mistrust in privacy and security online — including both perceptions and reported negative experiences — and reductions in selected online activities. We find that Internet-using households that expressed various privacy or security concerns or experienced an online breach or harassment were significantly more likely than their peers to report that such concerns led them to refrain from a range of online activities. After controlling for other factors, households citing identity theft as a major concern were 16 percentage points more likely to have declined to conduct a financial transaction online, while those concerned about data collection or tracking by government were 10 percentage points more likely to say they did not express a controversial or political opinion over the Internet. Furthermore, households that had experienced a data or security breach during the past year were 11 percentage points more likely to refrain from a financial transaction, and those experiencing online harassment were 14 percentage points more likely not to express a controversial view due to privacy or security concerns.It is clear that policymakers must better understand the prevalence of mistrust in the privacy and security of the Internet, as well as any resulting chilling effects. In addition to greatly concerning many Americans, privacy and security issues may lead to reductions in economic activity and the free exchange of ideas online. We hope our analysis will spark discussion of solutions — such as promoting strong encryption, transparency in privacy policies, and other best practices — that could help build trust in the Internet and stimulate the free flow of information and commerce.