The IRS Criminal Investigation Division is a part of the Internal Revenue Service (IRS), which is a government agency responsible for collecting taxes from people and businesses. The Criminal Investigation Division is responsible for investigating any cases where someone or a business may have done something illegal involving taxes. They look for things like not paying the amount of taxes that they owe, committing fraud or trying to hide income from the IRS. They also help with prosecuting people or businesses who did something illegal with their taxes.