Urea transporters (UTs) are a group of membrane channel proteins that specifically facilitate the permeation of urea, from bacteria to mammals, playing an essential role in urea reabsorption and water conservation. In mammals, there are two subfamilies of UT: the UT-A group originally isolated from the kidney inner medulla, and UT-B originally isolated from erythrocytes. The human UT-B gene (Slc14a1) arises from a single locus located on chromosome 18q12.1-q21.1, which is close to the UT-A gene (Slc14a2). The human Slc14a1 gene includes 11 exons, with the coding region extending from exon 4 to exon 11, and is approximately 30 kb in length. The rat Slc14a2 gene is very large, containing 24 exons, approximately 300 kb in length, and encodes 6 different isoforms. The Slc14a2 gene has two promoter elements: promoter I, located upstream of exon 1, drives the transcription of UT-A1, UT-A1b, UT-A3, UT-A3b, and UT-A4; promoter II, located within intron 12, drives the transcription of UT-A2 and UT-A2b. This chapter will summarize the evolution and genetic characteristics of UTs.