The complete germline organization of the β-chain genes of the murine T cell receptor was elucidated in order to obtain the structural basis for understanding the mechanisms of somatic DNA rearrangements. Twenty of the 22 known variable (Vβ) genes are clustered within 250 kilobases of DNA 5′ to the constant region (Cβ) genes. These V β genes share the same transcriptional orientation as the diversity (Dβ), joining (Jβ), and C β genes, which implies that chromosomal deletion is the mechanism for most Vβ to Dβ-Jβ rearrangements. Within this Vβ cluster, the distance between the most proximal Vβ gene and the Dβ-J β-Cβ cluster is 320 kilobases, as determined by field-inversion gel electrophoresis. The large distance between V β and Dβ, relative to that between D β and Jβ, may have significant implications for the ordered rearrangement of the T cell receptor β-chain genes.