This presentation was recorded prior to re:Invent. The twelve-factor application model is composed of twelve best practices for building modern, cloud-native applications. With guidance on factors like configuration, deployment, runtime, and multiple-service communication, the twelve-factor model prescribes practices that apply to everything from web applications to APIs and data-processing applications. Although serverless computing and AWS Lambda have changed application development, the twelve-factor methodology remains relevant and applicable in a serverless world. In this talk, we apply the twelve-factor model to serverless application development with Lambda and Amazon API Gateway, and we demonstrate how these services enable you to create scalable, well-built, low-administration applications.