The cerebellum is crucial for various associative sensorimotor behaviors. Delay 18 eyeblink conditioning (DEC) depends on the simplex lobule-interposed nucleus (IN) 19 pathway, yet it is unclear how other cerebellar modules cooperate during this task. 20 Here, we demonstrate the contribution of the vermis-fastigial nucleus (FN) pathway in 21 controlling DEC. We found that task-related modulations in vermal Purkinje cells and 22 FN neurons predict conditioned responses (CRs). Coactivation of the FN and the IN 23 allows for the generation of proper motor commands for CRs, but only FN output fine24 tunes unconditioned responses. The vermis-FN pathway launches its signal via the 25 contralateral ventral medullary reticular nucleus, which converges with the command 26 from the simplex-IN pathway onto facial motor neurons. We propose that the IN 27 pathway specifically drives CRs whereas the FN pathway modulates the amplitudes 28 of eyelid closure during DEC. Thus, associative sensorimotor task optimization 29 requires synergistic modulation of different olivocerebellar modules that provide 30 unique contributions.