Companies across industries are leveraging big-data analytics to enhance their products and services, improve marketing efforts and prevent fraud and abuse of their services. Big data offers substantial societal and public-health benefits, but companies must evaluate complex privacy and regulatory challenges when they are analyzing aggregated purchasing behavior, consumer online activity, or medical information for secondary uses. With input from in-house compliance professionals and outside counsel, this two-part article series offers practical guidance for designing big-data initiatives that ensure the legal and ethical use of big data across industries. This first part explores what big data is, how it is collected and used by various industries and applicable legal requirements. Part two will provide advice on remaining compliant while leveraging big data and strategies for dealing with big data and third-party vendors. See also “The FTC’s Big Data Report Helps Companies Maximize Benefits While Staying Compliant” (Feb. 3, 2016).