The main aim of this dissertation is to provide an analysis of the syntax of nominal modification based on the hypothesis that there is a group of DP-internal functional categories in addition to Gender/ Number Agreement Phrase that mediate between nouns (derived and non-derived) and their argumental and non-argumental modifiers. The common syntactic properties of restrictive modifiers such as adjectives, restrictive relative clauses and prepositional phrases in the two languages under study, Spanish and Southern uechua, are accounted for as properties of a functional projection Predicate Phrase internal to DP. The common morphosyntactic properties of argumental modifiers are accounted for as the properties of a DP-internal Person Agreement Phrase which is required to express subjecthood inside DP. Finally, the syntactic properties of a special class of nominal modifiers that includes adjectives in Spanish and quantifiers and suffixes in Southern uechua are accounted for as properties of two DP-internal functional projections, Mode Phrase and Aspect Phrase, that interact with the modality and aspectuality of the main clause. The data examined comes from Spanish and Southern uechua, two languages with opposite values in the Head Parameter; Spanish is a head-initial language whereas Southern uechua is head-final. It also includes different stages of Bilingual Spanish, the variety of Spanish spoken by native speakers of Southern uechua. The latter shows a gradual shift in the feature specification of the functional projections proposed.