A security clearance is a determination by the U.S. government that an individual can access classified information or data. There are three security clearance levels: confidential, secret, and top secret. Confidential is the lowest level of security clearance, and top secret is the highest. These levels correspond to the sensitivity of the information as classified by the government. Obtaining a security clearance requires passing a background investigation and must be renewed periodically. Some positions working for the federal government or a government contractor may require you to either hold an active security clearance or be able to obtain one. Because of the length of time it may take to obtain a security clearance, some employers may prefer candidates that already hold one that they obtained in a previous position. Fields may include information technology, software development, engineering, and finance.