The Spring Framework was created in 2003 by Rod Johnson, author of J2EE Development without EJB (Wrox Publishing, 2004). The Spring Framework was the response to all the complexity that the J2EE specifications had at that time. Today, it has improved, but you need to have a whole infrastructure to run certain aspects of the J2EE ecosystem. We can say Spring is a complementary technology to Java EE. The Spring Framework integrates several technologies, such as Servlet API, WebSocket API, concurrency utilities, JSON Binding API, bean validation, JPA, JMS, and JTA/JCA. The Spring Framework supports the dependency injection and common annotation specifications that make development easier. This chapter shows that the Spring Framework version 5.x requires a Java EE 7 level (Servlet 3.1+ and JPA 2.1) as the minimum. Spring still works with Tomcat 8 and 9, WebSphere 8, and JBoss EAP 7. Also, I show you the new addition to the Spring Framework 5— reactive support! Nowadays, Spring is one of the most used and recognized frameworks in the Java community, not only because it works, but because it continues to innovate with other amazing projects, including Spring Boot, Spring Security, Spring Data, Spring Cloud, Spring Batch, and Spring Integration, among others.