Mobile apps only account for about a fourth of online sales, as thousands of apps are vying for the attention of about 77 million mobile shoppers. The challenge is no longer just earning a user's attention—it's keeping it. The mobile environment is unique because a user's attention is much more scarce. A text message, a push notification, or a phone reminder will whisk them away. That's why the most successful e-commerce apps keep user onboarding focused and quick, guiding users through the one use-case that will bring them back for a second visit. This article explains how four of the most successful e-commerce apps engage users for the long haul.