Immunoglobulin A (IgA) production at mucosal surfaces contributes to protection against pathogens and controls intestinal microbiota composition. However, mechanisms regulating IgA induction are not completely defined. We show that soluble lymphotoxin α (sLTα₃) produced by RORγt⁺ innate lymphoid cells (ILCs) controls T cell–dependent IgA induction in the lamina propria via regulation of T cell homing to the gut. By contrast, membrane-bound lymphotoxin β (LTα₁β₂) produced by RORγt⁺ ILCs is critical for T cell–independent IgA induction in the lamina propria via control of dendritic cell functions. Ablation of LTα in RORγt⁺ cells abrogated IgA production in the gut and altered microbiota composition. Thus, soluble and membrane-bound lymphotoxins produced by ILCs distinctly organize adaptive immune responses in the gut and control commensal microbiota composition.