http://www.boozallen.com/insights/2016/10/enterprise-devops-playbook

If Agile software development (SD) had never been invented, we’d probably have little reason to talk about DevOps. However, there is an intriguing corollary worth pondering, as well: the rise of DevOps has made Agile SD viable. Agile is a development methodology based on principles that embrace collaboration and constant feedback as the pillars of its iterative process, allowing features to be developed faster and in alignment with what businesses and users need. However, operations today are generally moving at a pace that’s still geared toward sequential waterfall processes. As Agile SD took off, new pressures and challenges began building to address delivering new code into test, quality assurance, and production environments as quickly as possible without losing visibility and quality. We define DevOps simply as the culture, principles, and processes that automate and streamline the end-to-end flow from code development to delivering the features/changes to users in production. Without DevOps, Agile SD is a powerful tool but with a prominent limitation—it fails to address software delivery. As with other soft‐ ware development processes, Agile stops when production deployment begins, opening a wide gap between users, developers, and the operations team because the features developed for a time-boxed sprint won’t be deployed to production until the scheduled release goes out, often times many months later. DevOps enhances Agile SD by filling this critical gap, bridging operations and development as a unified team and process.