The bloodstream and the central nervous system (CNS) are separated by the blood–brain barrier (BBB), an intricate network of blood vessels. Its main role is to regulate the environment within the brain. The primary obstacle for drugs to enter the CNS is the low permeability of the BBB, presenting a significant hurdle in treating brain disorders. In recent years, significant advancements have been made in researching methods to breach the BBB. However, understanding how to penetrate the BBB is essential for researching drug delivery techniques. Therefore, this article reviews the methods and mechanisms for breaking through the BBB, as well as the current research progress on this mechanism.