Add some : The JRE package is intended for distribution with applications. It does not contain the tools.jar file that has the compiler and other command line tools. The reason Sun makes the distinction is to give developers a more compact set of files to distribute with a product. Also, JVM is the more generic name which can apply to any program which obeys the Java Virtual Machine Specification - whether it's made by Sun, IBM, Microsoft, or whoever. JRE on the other hand is the name for Sun's implementation of a JVM.