JSLIM -- computational morphology in the framework of the SLIM theory of language. JSLIM is a software system for writing grammars in accordance with the SLIM theory of language. Written in Java, it is designed to facilitate the coding of grammars for morphology as well as for syntax and semantics. This paper describes the system with a focus on morphology. We show how the system works, the evolution from previous versions, and how the rules for word form recognition can be used also for word form generation. The first section starts with a basic description of the functionality of a left associative grammar and provides an algebraic definition of a JSLIM grammar. The second section deals with the new concepts of JSLIM in comparison with earlier implementations. The third section describes the format of the grammar files, i.e., of the lexicon, of the rules and of the variables. The fourth section broaches the subject of the reversibility of grammar rules with the aim of an automatic word form production without any additional rule system. We conclude with an outlook on current and future developments.