This chapter discussed a small range of the new class loaders that were first implemented in JBoss 7 and remained in WildFly due to its wide acceptance, performance, and friendly structure. One of the positives is the reduction of errors in class loading, which was in fact a big headache when these errors occurred in the previous versions of JBoss AS. The concept of modules is connected directly to a subdeployment. For example, each JAR, WAR, or EAR file is considered as a subdeployment and each has its own class loader, unless this is explicitly configured as discussed in this chapter. We have seen that, in a module, we can include one or more libraries; it helps us to group several libraries. Our application needs only one module and a dependency defines this application. We have also seen what the global modules are and how they work.