Online marketplaces such as eBay, Uber, and Airbnb have the potential to reduce racial, gender, and other forms of bias that affect the off-line world. And in the early days of internet commerce, the relative anonymity of transactions did make it harder for participants to discriminate. But as listings began to include photos, names, and other means of identification, bias emerged in areas ranging from labor markets to credit applications to housing—sometimes made worse by a lack of regulation, the absence of in-person interactions, and the use of automation and big data. How can companies reverse the tide?