This part of the Guidelines is an overview of the proposed methodology for assessing the impacts and costs of forced displacement. It provides the background and context for the methodology and presents a summary of key principles in the approach. Section 1 explains why the Guidelines were developed – to meet the need for enhanced understanding and evaluation of the economic and social aspects of forced migration. This section also introduces the flexible approach we recommend to using the Guidelines, requiring adaptation to local circumstances and needs. Section 2 explains key aspects of the approach, such as the need to combine quantitative and qualitative methods, and the main areas of use of the Guidelines. It summarises the benefits of agency collaboration and of pragmatic approaches to making the best use of available data.