Do people have trouble with registration or sign-in for your app? How often do potential customers use the "Forgot password?" button or give up completely when trying to create an account? In user experience research at Google and throughout the industry, we've found that over half of people seeing a sign-in page will fail to authenticate, ranging from making typos to creating duplicate accounts. Building a secure and usable auth experience is complex and difficult. But there are some simple principles of good authentication user experience design that can make things a lot easier. We'll discuss examples that you can apply in your app, from tips for effective UI to techniques for secure, password-less authentication built on open standards and APIs available on Android that make account creation as easy as one-tap, and keep users signed-in across devices automatically. Make the most of your app installs and never lose someone at the account screen again. Keep your users engaged when they come back on another device by showing them their content as soon as they open the app and resuming activities right away. And make it all a secure experience that protects user data.