This chapter describes how the concept of hydric soils was developed over about a 10-year period and how it continues to develop as we learn more about the processes that lead to the formation of wetland soils. The discussion has been broken into three major sections: (1) the background of the development of hydric soils, (2) the evolving nature of the definition, and (3) the concept of hydric soil field indicators. In the background section, we cover the initial activities of the development of hydric soils through the publication of the first national list of hydric soils. In the section on the evolving nature of hydric soils, we discuss the impact of legislation on the development of hydric soil criteria and definition. And finally, we discuss the concept and use of hydric soil indicators in the identification of hydric soils in the field.