This book examines the U.S.-foreign partnership efforts to prevent nuclear smuggling and terrorist travel. The National Nuclear Security Administration (NNSA) established the Megaports Initiative in 2003 to deter, detect, and interdict nuclear or other radiological materials smuggled through foreign seaports. The Initiative funds the installation of radiation detection equipment at select seaports overseas and trains foreign personnel to use this equipment to scan shipping containers entering and leaving these seaports, regardless of destination. Additionally, the U.S. government has identified four key gaps in foreign countries' capacity to prevent terrorist travel overseas. The book evaluates how U.S. capacity-building efforts address those gaps and assesses the extent to which the U.S. government is measuring progress in its efforts to close those gaps.