The majority of climate change impact assessments focus on potential impacts at the local/regional scale. Climate change scenarios with a fine spatial resolution are essential components of these assessments. Scenarios must be designed with the goals of the assessment in mind. Often the scientists and stakeholders leading, or participating in, impact assessments are unaware of the challenging and time-consuming nature of climate scenario development. The intent of this review, presented in two parts, is to strengthen the communication between the developers and users of climate scenarios and ultimately to improve the utility of climate impact assessments. In Part I, approaches to climate downscaling are grouped into three broad categories – dynamic downscaling, empirical-dynamic downscaling and disaggregation downscaling methods – and the fundamental considerations of the different methods are highlighted and explained for non-climatologists. Part II focuses on the application of climate change scenarios.