After introducing functional and system modules we discuss module hierarchies. Several predefined modules such as Booleans, machine integers, quoted identifiers, and so on are also described. The reflective aspects of Maude, and the related topic of internal rewriting strategies--that is, strategies that can be defined with rewrite rules at the metalevel--are explained in detail. Parsing issues, as well as the input/output facilities provided by the LOOP-MODE module are also treated in detail. We finish the section with a discussion of system issues and debugging.