The interstate slave trade refers to the legal commerce of enslaved people across state lines within the United States, primarily occurring in the 19th century. This trade was a critical aspect of the domestic slave system, as it facilitated the transfer of enslaved individuals from slave-holding states in the Upper South to the plantation economies of the Deep South, where labor demand was higher. The interstate slave trade not only reinforced the institution of slavery but also shaped social and economic structures in both regions involved.