The presentation concerns the XML architecture assumed for the IPI PAN Corpus of written Polish, being created at the Institute of Computer Science of Polish Academy of Sciences. The design of this corpus implements the principles laid out by the XCES Guidelines (see e.g. Ide et al. 2000), featuring in particular the so-called stand-off annotation, whereby each text is split into several components residing in separate XML files that may instantiate various DTDs or XML Schemas. More specifically, each text in the IPI PAN Corpus will be composed of three layers, as sketched below. main file <- sentence segmentation file <- morphosyntactic annotation file The main file contains the actual text with gross structural markup down to the level of the paragraph, and with the addition of tags signalling quotations and various aspects of text highlighting (italics, small caps, etc.). The next document establishes the sentence boundaries and may act as a base for another layer of annotation, or for a document that aligns sentences from different versions of the base text (for the purpose of creating a parallel corpus and thus reusing the text resources in the future). It also resolves the tags indicating text highlighted in the main file, classifying the information conveyed by e.g. italics as 'foreign text', 'proper name', 'emphasis', etc. The third layer of annotation contains the (often multiple) outputs of the morphological analyser (morphosyntactic information, lemmas) and the output of the disambiguator. This setup creates interesting questions, relating e.g. to cost-effectiveness of corpus creation, or structuring the data model that underlies the various possible types of annotation. Thus, the multiple-layer architecture of the corpus does not only reflect the logical divisions among the kinds of data visualised by the relevant annotation files -- it is also geared towards the issue of reusability and extensibility of corpus annotation. Additionally, as the creation of the outer levels of annotation proceeds, the need for human intervention increases, which means that at early stages of the project, the corpus will consist of the innermost layers of annotation only ('main files'), as these can sometimes be created fully automatically. The additional layers will be provided later, at an obvious cost. The presentation will be illustrated with fragments of a mini-corpus of Polish designed to incorporate the major architectural features of the IPI PAN Corpus. Related link: