Hindawi Publishing Corporation Advances in High Energy Physics Volume 2010, Article ID 196714, 93 pages doi:10.1155/2010/196714 Review Article Unquenched Flavor in the Gauge/Gravity Correspondence Carlos N ´ u˜ nez, 1 ´ Angel Paredes, 2 and Alfonso V. Ramallo 3 1 Department of Physics, University of Swansea, Singleton Park, Swansea SA2 8PP, UK 2 Departament de F´ ısica Fonamental, ICCUB Institut de Ci` encies del Cosmos, Universitat de Barcelona, Mart´ ı i Franqu` es 1, 08028, Barcelona, Spain 3 Departamento de F´ ısica de Part´ ıculas, Instituto Galego de F´ ısica de Altas Enerx´ ıas (IGFAE), Universidade de Santiago de Compostela, 15782, Santiago de Compostela, Spain Correspondence should be addressed to Alfonso V. Ramallo, alfonso@fpaxp1.usc.es Received 26 February 2010; Accepted 25 May 2010 Academic Editor: Radoslav C. Rashkov Copyright q 2010 Carlos N ´ u˜ nez et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Within the AdS/CFT correspondence, we review the studies of field theories with a large number of adjoint and fundamental fields, in the Veneziano limit. We concentrate in set-ups where the fundamentals are introduced by a smeared set of D-branes. We make emphasis on the general ideas and then in subsequent chapters that can be read independently and describe particular considerations in various different models. Some new material is presented along the various sections. 1. Introduction, General Idea, and Outline 1.1. Introduction and Outline The AdS/CFT conjecture originally proposed by Maldacena 1, 2, refined in 3, 4 and reviewed in 5, has been one of the most interesting developments in theoretical physics of the last decades. It has become one of the most powerful analytic tools to deal with strong coupling effects of some particular gauge theories in the planar limit N c → ∞. The most studied and best understood case corresponds to SUN c N  4 SYM which is a highly supersymmetric conformal theory and which only contains matter in the adjoint representation of the gauge group. Certainly, there are many interesting field theories which do not share these properties and this fact has lead to an enormous amount of effort devoted to extending the duality along different paths. Consequently, people have constructed gravity duals of nonsupersymmetric, non-conformal gauge theories, in different vacua and with