Building highly interactive software that users love to use is usually a challenging endeavor. However, the open source Flex SDK and Java are a perfect combination of technologies for building very rich and highly interactive software for the Web and the desktop. The communication between the Java back–end and Flex front–end can utilize a number of different communication protocols, but the easiest and best performing is the open source BlazeDS library. This session covers the fundamentals of using Flex, Java, Spring, and BlazeDS to build rich and highly interactive software for the Web and the desktop.