This chapter provides practical advice for scientists conducting clinical nutrition research. We recognize that, while many investigators do not have the resources to conduct large-scale, multicenter studies, there is great merit in smaller studies for many reasons that include gathering essential pilot data to justify larger studies and conducting experiments that can require intensive subject participation or gaining a better understanding about mechanisms of action. For example, well-designed clinical studies can advance the fi eld by identifying subgroups of patients with the largest response to a given intervention by testing implementation of a specifi c diet intervention in free living subjects and by suggesting potential mechanisms that explain the diet response. In Table 41.1, we have included a number of important resources that describe the key aspects of designing and conducting clinical studies. These books and journal articles provide detailed and comprehensive information regarding all aspects of conducting nutrition research with human participants. However, there are many novel study designs with inherent challenges in defi ning participant populations, food or supplement distribution, and diet design. For the most part, these issues have not been discussed in detail in the references listed in Table 41.1. In Table 41.2 are listed online resources for information needed for the Institutional Review and Protection of Human subjects. In Table 41.3 to Table 41.10 and Figure 41.1, we provide a variety of forms developed at the Metabolic Diet Study Center at Penn State University that we have used for our human studies research. Other investigators may fi nd these useful and will want to adapt them for their own purposes. Finally, we discuss emerging trends in biological science with important implications for clinical nutrition.