Proinflammatory T helper 1 (Th1) cells express high levels of carbohydrate ligands for the endothelial selectins, but the molecular basis for this phenotype is incompletely understood. We document here a significant role in selectin ligand formation for the recently described Th1 transcription factor T-bet. Th1 cells generated from T-bet-/- mice showed significantly lower levels of ligands for both E-selectin and P-selectin, compared with wild-type (WT) Th1 cells. Enforced expression of T-bet in WT Th0 cells only modestly up-regulated P-selectin ligands and had no effect on E-selectin ligands. To define a mechanism for the defects observed in T-bet-/- mice, we examined expression of glycosyltransferases involved in selectin ligand biosynthesis. T-bet-/- Th1 cells expressed significantly lower levels of core 2 β1,6 N-acetylglucosaminyltransferase I (C2GlcNAcT-I), but no differences in levels of α 2,3-sialyltransferase IV (ST3Gal-IV). Further, we show that T-bet is responsible for the signal transducer and activator of transcription 4 (Stat4)–independent increase in Th1 cells of fucosyltransferase VII (FucT-VII). We also identify ST3Gal-VI, which is thought to play an important role in E- and P-selectin ligand formation, as an interleukin 12 (IL-12)–regulated, T-bet–dependent gene. These data show that T-bet controls selectin ligand formation in Th1 cells via control of expression of multiple key enzymes in response to IL-12 signaling and establishes an independent transcriptional pathway for control of Th1 cell traffic.