For a small category D we define fibrations of simplicial presheaves on the category D × ∆, which we call localized D-left fibration. We show these fibrations can be seen as fibrant objects in a model structure, the localized D-covariant model structure, that is Quillen equivalent to a category of functors valued in simplicial presheaves on D, where the Quillen equivalence is given via a generalization of the Grothendieck construction. We use our understanding of this construction to give a detailed characterization of fibrations and weak equivalences in this model structure and in particular obtain a Yoneda lemma.We apply this general framework to study Cartesian fibrations of (∞, n)-categories, for models of (∞, n)-categories that arise via simplicial presheaves, such as n-fold complete Segal spaces. This, in particular, results in the Yoneda lemma and Grothendieck construction for Cartesian fibrations of (∞, n)categories. CONTENTS 0. Introduction 1 1. A Deep Dive into Enrichments and Some Fibrations 8 2. From Left Fibrations to D-left Fibrations 29 3. Grothendieck Construction for D-Simplicial Spaces 39 4. Localized D-Left fibrations 57 5. (Segal) Cartesian Fibrations of (∞, n)-Categories 86 6. What needs to be done? 102 References 104