21st Century Problems cannot be solved with 20th Century software architectures. So why is the starting point for so many projects built on the assumption of a simplistic monolithic, three-layer architecture sat on top of a RDBMS? Hardware has progressed. It has changed many of the assumptions that such architectures were built upon. Modern systems are distributed, deal with massive throughput of data and transactions. Users expect 24/7 service. The Reactive Manifesto describes what it takes to build systems that meet these demands. Such systems are Responsive, Resilient, Elastic and Message Driven. What does this mean in terms of software architecture and design? This presentation will introduce these ideas and describe how systems built on these principles work.