This article presents a project aiming at the construction of a large morphosyntactically and structurally annotated corpus of Polish. The project, realized at the Institute of Computer Science, Polish Academy of Sciences between April 2001 and March 2004, is partially financed by the State Committee for Scientific Research (KBN). While particular solutions concerning the linguistic and XML annotation of natural language texts are presented in three separate articles in this volume, this article describes the origin of the project, its scope and some envisaged applications of the results of the project.