Fetal exposure to drugs/xenobiotics can be dependent on metabolism and transport by the placenta. To assess developmental toxicities of drugs/xenobiotics, it is critical to understand the mechanisms that control metabolism and trafficking of drugs/xenobiotics across the placental barrier. This workshop highlights the most recent knowledge of the interactions of drugs and xenobiotics with transporters and drug-metabolizing enzymes in human placenta. The purpose of this symposium is to bring together experts in drug transport/metabolism and toxicology to highlight the mechanisms that control drug/xenobiotic disposition in the placenta and impact on fetal drug/xenobiotic exposure and response.