This three-year PhD study looks at heritage performance in impact assessment (IA) practices, analysing the urban planning context and management experiences of selected urban World Heritage (WH) sites in the UK. The research develops recommendations for assessing the impact of plans, programmes and projects on heritage values in culturally significant urban areas with the emphasis on Strategic Environmental Assessment (SEA) and Environmental Impact Assessment (EIA) of large-scale projects in an urban environment. The research analyses theoretical and empirical approaches to heritage management, investigates methodologies for heritage IA and explores opportunities for and barriers to improved heritage IA in the context of current UK policy. In particular, the research contributes with the conceptual framework of identification, interpretation and management of the cultural heritage in the urban planning system. The review of academic and other relevant literature helped to develop the conceptual framework. The data was collected by means of desk-based documents analysis, case studies, focus-group seminars and an on-line Questionnaire with the experts in the heritage and IA fields. The world’s most well-known and arguably most protected sites with officially identified Outstanding Universal Value – WH sites – provide general lessons for the heritage management and IA of new developments and infrastructure projects. The management of UK WH sites could be said to have the features of what is known as a values-based approach to conservation. This approach emphasises the identification of cultural heritage significance with the early participation of different stakeholders in the planning process; the latter has a scope for improvement in the UK context. Research on the boundaries of the heritage and IA fields leads to an improved understanding of cultural heritage and provides a framework for the IA process. The developed framework and the criteria for an enabling environment could be useful for achieving agreement between the different stakeholders, and could allow a smoother planning decision-making process, leading in turn to a reduced need for monitoring from international bodies. The results are useful for planners and developers in the context of western practice, and could also be relevant to the development of international guidelines.