The transformation and manipulation of XML is an increasingly important research topic. This paper examines a number of issues with regard to languages for transforming and reacting to changes on XML data. On the transformation side, we focus on XSLT, a powerful language for converting XML data into other formats. We look at analysis and optimisation issues for XSLT, as well as support for debugging and automatic generation. On the reactivity side, we focus on an event-condition-action rule approach, which is a natural candidate for the support of reactive functionality on XML repositories.