As pen-based computing becomes more prevalent, it is increasingly important to be able to share ink across ap- plications and across platforms. The emerging standard Ink Markup Language (InkML) is intended for this purpose. Four drafts of the proposed standard have been produced since 2003, resulting in a specification with broad input from industry and invited experts. The last working draft has simplified and generalized the specification in some im- portant ways and the specification is now in "last call" sta- tus. This paper presents an overview of the main features of InkML, with an emphasis on the rationale for what has changed for the last call version.