This paper critically discusses the use of Extensible Markup Language (XML) for agile supply chains and proposes practical guidelines and future research directions for the field. XML has been identified by many as a prominent technology for enabling electronic supply chain integration, but the adoption of it in the industry has been rather slow and limited. This paper discusses the factors that enable agility in supply chains, and explains why XML is the best candidate for facilitating such factors. Then the major XML-based integration initiatives such as ebXML, RosettaNet, and Web Services are diagnosed in terms of their pros and cons for supply chain agility, as well as the reasons for their slow diffusion. Based on the discussion, this paper proposes that: the integration efforts need to first focus on the industries that need agility; stringent business process standards are necessary; and implementation should be made much easier and more affordable for small and medium enterprises (SMEs). Further research issues are also suggested based on the discussion.