The paper mainly focuses on the institutional performance of İzmir Development Agency (İZKA) for İzmir Regional Plan 2010-2013 activities. Main objective of the research has been to assess the extent of İZKA's performance for the implementation of Regional Plan in the context of its organizational structure. Theoretical findings indicated that institutional settings have played significant roles in shaping regional development. In this sense, this study relates to two bodies of literature, i.e. institutional theories and their transition to regional development field. Clearly institutional approaches have attracted considerable attention for the last three decades. Although a great deal of views offered broad and complex definitions, institutions were mostly expressed through two interconnected forces comprising in formal, i.e. laws, rules, regulations, organizations as well as informal, i.e. human behaviour, social norms, community actions, conventions. Even though the contents of institutions evolve under changing conditions, through space and over time, Scott (1995, 2004) follows up a comprehensive and multi-disciplinary way by considering institutions under three elements, i.e. regulative, normative and cognitive. While regulative elements mostly reflects formal sides of institutions, normative and cognitive elements mostly emphasizes social obligations in accordance with informal aspects. According to this approach, most economists and those constitute rationalist approaches to institutional theory dominate the regulative side of institutions (Mayer, 2003; North, 1990; Scott, 2004) whereas recent sociologists, political scientists and those who approach this issue from other disciplines emphasize the cognitive and normative sides (Amin and Thrift, 1995; Morgan, 1997; Scott, 1998, 83-8; Lakshamanan and Button, 2009). This paper is concerned with the institutional building efforts and their transition into regional policy. The reviews developed within this framework put forward the argument that institutions have long been neglected in the regional policy action. In this context it has been argued that prior to the 1970s, regional issues were weakly institutionalized. This period failed to integrate institutional settings and regional development. Then, it has been discussed widely whether institutions matter in development, and thus cause growth or not. During the period between 1970s and 1990s, institutions became a focal point for regional development policies along with the rising significance of regions in a globalizing world. Currently, however, assessing what kind of institutions are to be created for regional development for more effective plans and successful implementation processes needs to be discussed. Subsequently, an emphasis underlying the diversity of institutions and their comprehensive perspectives in regional development and initial attempts for institutional building at regional level came to the forefront in policy and practice since the 1990s. Theoretical grounds have accordingly shaped the regional policy in Turkey with respect to institutional restructuring process, too. The issues of regional disparities and regional competitiveness have been one of the significant problem areas for years. Regarding this, various policies and tools have been developed to decrease regional disparities and to accelerate local and regional development. Following regional development trajectories around the world, regional policy activities have gained momentum in Turkey, as well. Thereby, regional development plans, called as The South-eastern Anatolia Project (GAP), The Zonguldak- KarabükBartın Regional Development Project (ZBK), The Eastern Anatolia Project (DAP), The Eastern Blacksea Regional Development Plan (DOKAP) and The Yeşilırmak River Basin Project were formulized. However, these plans, particularly dominated by the central system could not been implemented adequately with the exception of GAP. Although comprehensive and integrated regional planning approaches were adopted, the attempts remained limited due to the lack of institutional capacity at regional level. Due to the already experienced policy failures, building necessary institutional mechanism at regional level was necessitated. It was claimed that Europeanization process made a cross-cutting impact on weaker local system, resulted from the enhancement of regional institutional infrastructure in shaping and organizing regional development. Driven by the alignment process of regional policies to the EU norms, a more regionalized and decentralized model has entered into the Turkey's regional political agenda. It has been an important step from a centralized state towards a multi-level governance model. In this context, the arrangement of NUTS classification in accordance with the EU's statistical regional structure was firstly defined and subsequently, 26 Development Agencies (DAs), which were derived from NUTS-II regions, were established with the Decrees of Council of Ministers as a result of top-down political action. Thus, Turkey's centralized structure has been challenged by the enactment of The Law on The Establishment and Duties of Development Agencies (No: 5449). After the completion of DAs, SPO (State Planning Organization) asked agencies to prepare strategic regional development plans (2). For the first time, the responsibility for preparation of regional plans was given to DAs in Turkish history. Thus, first regional plan was produced at regional level by İZKA and İzmir Regional Plan 2010-1013 was approved by SPO on 16.06.2010. In order to assess currently existing institutional performance of DAs in regional plan activities, İZKA has been undertaken as a case study area by using a number of criteria. Although the institutionalization of DAs needs a long process, when considered İzmir Region; a series of drivers have shorten this long process of İZKA. These major derivers are mainly its local powers including both private and public sector, its institutional arrangements which is also a leading region of Turkey, the rising level of local activism from the early 1990s and endogenous dynamics of the region. After the determination of İZKA, this study was designated into two stages. In the first stage, factors that shall attribute institutional performance were identified in the light of institutional approaches. In the second stage, the performance of İZKA was assessed over these factors. The effectiveness of İZKA in performing Regional Plan was handled in terms of internal and external effects of this Plan.