A Treebank is a text corpus in which each sentence has been annotated with its syntactic structure. Although the construction of a treebank is an expensive task, we believe that it is indispensable for the development of real applications in the field of Natural Language Processing (NLP) and also for the development of the Information Society. At a purely linguistic level, the Treebank is an essential database for the study of a language given that it provides analyzed/annotated examples of real language. The linguistic study directly results in an improvement in the quality of several applications, such as Part-Of-Speech (POS) taggers and parsers (Collins 1997, 2000; Charniak 2000), because it provides common training and testing material allowing different algorithms to be compared and improved. In the last few years, treebank corpora such as the Penn Treebank (Marcus et al., 1993) and the Prague Dependency Treebank (Bohmova et al. 2003) have become a crucial resource for building and evaluating natural language processing tools and applications. As Abeille (2003) sets out, there are efforts underway for Czech, German, French, Japanese, Polish, Spanish and Turkish, to name just a few. In Kakkonen (2005) we can find the state of the art of dependency-based treebanks. The Basque Dependency Treebank (BDT) is actually the Reference Corpus for the Processing of Basque (EPEC) annotated at syntactic level. The EPEC is a 300,000 word corpus of standard written texts which aims to be a training corpus for the development and improvement of several NLP tools. It has been manually tagged at different levels: morphology, lemmatization and surface syntax (Aduriz et al. 2006). The next level of tagging —annotation of dependency relations— is currently being carried out in BDT. In this paper, we describe the annotation of noun phrase (henceforth, NP) constructions in detail following the Dependency Grammar theory (Tesniere 1959). For a better understanding of our work it should be noted that for us, NP is a purely descriptive term. We are not concerned with understanding the internal structure of NPs. The syntactic description of Basque NPs has been mainly developed within the generative framework by Goenaga (1980), Eguzkitza (1993), Laka (1993), Artiagoitia (2002),