The Medical College Admission Test® (MCAT®) is a standardized, multiple-choice examination designed to assess the examinee's problem solving, critical thinking, writing skills, and knowledge of science concepts and principles prerequisite to the study of medicine. Scores are reported in Physical Sciences, Verbal Reasoning, Writing Sample and Biological Sciences.
Almost all U.S. medical schools require applicants to submit MCAT exam scores. Many schools do not accept MCAT exam scores that are more than three years old.
Up to date information about the MCAT can be found at https://www.aamc.org/students/applying/mcat/.
This website has links for registering for the exam, as well as advice on preparation.