As hackers phish their way into SMS messages with one-time passcodes or use photos of fingerprints or eye veins to bypass biometric factors, developing effective online multi-factor authentication (MFA) systems is becoming more difficult. Using two or even three ways to establish identity online is particularly significant in the financial sector, where failure to secure the accounts of clients or employees can lead to massive losses. Online authentication factors must not only be secure, but also convenient for the user and, of course, make economic sense. In this first part of our two-article series, we explore the MFA landscape for the financial sector, strategies for ensuring both security and user friendliness, challenges that certain factors present and the means to overcome those challenges. In the second part, we will discuss MFA innovations, including those from the Fast Identity Online Alliance, what regulators expect around the world, and how companies can economically implement an MFA system. See also “Finding the Best Ways to Secure Digital Transactions in a Mobile World” (Oct. 19, 2016).