Bar admission is regulated by each state's board of bar examiners. Bar requirements are state-specific and vary from state to state, so it's important to check the requirements for the jurisdiction in which you plan to practice law.
The National Conference of Bar Examiners (NCBE) is the organization that produces the five multistate bar examinations. The NCBE site contains a wealth of information and should be at the of your bar prep resource list.
This publication is produced annually by the NCBE in collaboration with the ABA. It contains current information on bar admission requirements in all U.S. jurisdictions, including a directory of state bar admission agencies. It is available in pdf for free at the link above.