In Editorial Studies, documenting the work of an editor, e.g. by creating critical comments and explanatory notes while reconstituting and analysing original documents, is a central task. However, a conceptual distinction between different types of such annotations is often lacking. This chapter proposes a distinction that is based on document theory and modelling approaches that cover the digitization and processing of documents. In summary, a distinction is made between ‘commentaries’, which justify the determination of the form of a document, and ‘explanatory notes’, which assist in conveying a document to an assumed readership. A technical implementation of the proposed annotation model for critical editions is presented on the basis of common document description languages in digital publishing.