A language module is the collection of language constructs whose concepts and operations are closely related. This paper demonstrates how to use action semantics to define and extend language modules. We first define a language module for an expression language core, and then language modules for bindings, block structures, parameters, and higher-order expressions. Finally, we show that the language modules can be combined, if there is no violation of uniformity and orthogonality, to become a more complex language module.