Kittens appear visually immature at eye opening and studies were conducted to trace changes with maturity. Longitudinal determinations of optical quality indicate that optical factors may not limit visual performance in young kittens. Estimates of visual axis alignment in alert kittens at various ages show that functional visual divergence does not occur even when the pupillary axes are divergently misaligned. It is thus possible that fused binocular vision may occur in very young kittens, suggesting that procedures that disrupt binocularity may have effects at the cortical level. Single-unit analysis of striate cortex in kittens monocularly deprived for varying periods during the first three postnatal weeks confirms this possibility. Effects are also found for kittens reared with monocular defocus to simulate anisometropia. Binocular recovery from the effects of monocular deprivation is found to be quite limited in kittens given binocular exposure following unilateral lid-suture. The recovery that occurs requires active visual input rather than a cessation of imbalance in the two eyes. A long period of binocular exposure appears to be ineffective in restoring binocular connections in a cat reared with optically induced strabismus.