The Hydrogeomorphic (HGM) Approach is a collection of concepts and methods for developing functional indices and subsequently using them to assess the capacity of a wetland to perform functions relative to similar wetlands in a region. The approach was initially designed to be used in the context of the Clean Water Act Section 404 Regulatory Program permit review sequence to consider alternatives, minimize impacts, assess unavoidable project impacts, determine mitigation requirements, and monitor the success of mitigation projects. However, a variety of other potential applications for the approach have been identified including: determining minimal effects under the Food Security Act, designing mitigation projects, and managing wetlands. This report uses the HGM Approach to develop a Regional Guidebook for assessing the functions of low gradient, riverine wetlands in western Kentucky. The report begins with a characterization of low gradient, riverine wetlands in the western Kentucky, then discusses (a) the rationale used to select functions, (b)the rationale used to select model variables and metrics, (c) the rational used to develop assessment models, and (d) the data from reference wetlands used to calibrate model variables and assessment models. Finally, it outlines an assessment protocol for using the model variables and functional indices to assess low gradient, riverine wetlands in western Kentucky.