RuleML is a markup language developed to express both forward (bottom-up) and backward (top- down) rules in XML for deduction, rewriting, and further inferential-transformational tasks. It is defined by the Rule Markup Initiative, an open network of individuals and groups from both industry and academia that was formed to develop a canonical Web language for rules using XML markup and transformations from and to other rule standards/systems. One or more rule engines will be needed for executing RuleML rulebases. On 2000-11-15, the RuleML Initiative thus joined forces with the Java Specification Request. This cooperation will enable a direct cross-fertilization between the specifications of the open XML-based Rule Markup Language and of the Java runtime API for rule engines.