Buckwheat is a traditional food widely utilized throughout the world. Buckwheat contains some nutritionally beneficial components at high levels and may have many characteristics as a functional food. This chapter describes various characteristics of buckwheat as an important and traditional food. Buckwheat belongs to the Polygonaceae family and is taxonomically distant from the Gramineae family to which cereals such as rice, wheat, and maize belong. However, buckwheat seed has chemical and utilization characteristics similar to cereal grains, and thus is usually classified as a cereal. It is often alternatively classified as a pseudocereal. Buckwheat is mainly classified into three types with respect to harvesting season: summer type, autumn type, and middle type. This classification may be due to susceptibility to the day length. Buckwheat breeding has been extensively discussed. Chloroplast DNA analysis in buckwheat species has shown that the DNA of Fagopyrum esculentum is phylogenetically distant from those of Fagopyrum tataricum and Fagopyrum cymosum. Evaluation of genetic variability among common buckwheat populations has shown that the dendrogram separates accessions into a European group and an Asian group.