The informational capabilities and utility of Big Data — defined as large data sets capturing broad and deep information — are fundamentally al- tering the theory and practice of competition policy and law. While there is nothing novel about restrictions on inter-firm exchange of competitively sensitive information, Big Data allows for advertent and inadvertent sharing at scales not previously available. We have long known that horizontally competing firms cannot share customer or pricing information with im- punity. This has always been so — and has long informed antitrust policy and practice. We also have known that firms in possession of unique or essential inputs may be subject to particular competition law scrutiny; or how firms with what one may characterize as market power may act in certain contexts may also be subject to particular scrutiny. Big Data pro- vides tools and capabilities for firms that enable efficient conduct, but also may disadvantage rivals. The landscape enabled by Big Data has revealed emerging competitive concerns.