T follicular helper (T FH) cells are specialized effector CD4 + T cells that help B cells develop germinal centers and memory. However, the transcription factors that regulate T FH differentiation remain incompletely understood. Here we report that selective loss of either Lef1 (LEF-1) or Tcf7 (TCF-1) resulted in T FH defects, while deletion of Lef1 and Tcf7 severely impaired T FH differentiation and germinal centers. Forced expression of LEF-1 enhanced T FH differentiation. LEF-1 and TCF-1 coordinated T FH differentiation by two general mechanisms. First, they established the responsiveness of naïve CD4 + T cells to T FH signals. Second, they promoted early T FH differentiation via the multipronged approach of sustaining expression of IL-6Rα and gp130, enhancing ICOS expression, and promoting expression of Bcl6.