The Galβ1-3GlcNAc linkage (type 1 chain) is widely found on glycolipids and N-linked and mucin-type O-linked glycoproteins primarily in cell types derived from the endoderm (Oriol et al. 1986). In contrast, the Galβ1-4GlcNAc linkage (type 2) is widely distributed on glycolipids and glycoproteins derived from the ectoderm and mesoderm. Type 1 chain constitutes cores for the Lewis blood group antigens including structures such as Le^a and Le^b and the corresponding ABH structures (Clausen and Hakomori 1989). Type 1 chain also carries classical cancer-associated structures such as sialyl-Le^a (N19-9) (Magnani et al. 1982) and disialyl-Le^a (FH7) (Nudelman et al. 1986). The type 1 chain core is catalyzed by β3galactosyltransferases (β3Gal-T) and distinct β3Gal-T activities with βGlcNAc substrates were first described in the 1980s (Sheares and Carlson 1983; Sheares et al. 1982) and shown to be distinct from β4galactosyltransferase (β4Gal-T) activities (Holmes 1989; Sheares and Carlson 1983). The first β3Gal-T gene cloned, β3Gal-T1, was identified by expression cloning (Sasaki et al. Japanese patent JP1994181759-A/1). Subsequently, this gene sequence was used to probe emerging EST and gene sequences early in the human genome project and unravel the large β3glycosyltransferase gene family assigned to CAZy family GT31. This family includes three β3Gal-Ts (T1, T2, and T5) catalyzing the Galβ1-3GlcNAc linkage as well as a large number of other β3GalNAc-Ts, β3GlcNAc-Ts (for reviews see Amado et al. 1999; Togayachi et al. 2006). This review summarizes the properties of the first two cloned and expressed β3Gal-Ts, β3Gal-T1 and T2.