Technical Abstract: Recent progress in determining the bioconversion of dietary provitamin A carotenoids to vitamin A is reviewed here. Methods for assessing the bioavailability and bioconversion of provitamin A carotenoids have advanced significantly in the last 10 years, specifically through the use of stable isotope methodology, which includes the use of labeled plant foods. The effects of the food matrix on the bioconversion of provitamin A carotenoids to vitamin A, dietary fat effects, and the impact of genotype on absorption and metabolism of beta-carotene have been reported recently. A summary of the major human studies that determined conversion factors for dietary beta-carotene to retinol are presented here, and these data show that the conversion efficiency of dietary beta-carotene to retinol is in the range of 3.6 – 28 to 1 by weight. There is a wide variation between conversion factors reported in different studies, but also between individuals in a particular study. These findings show that the vitamin A value of individual plant foods rich in provitamin A carotenoids may vary significantly and are in need of further investigation.