DWI is short for “driving while intoxicated”. It is also known as DUI, or “driving under the influence”. You are driving while intoxicated if you are behind the wheel of a motor vehicle and have had enough to drink to influence your blood alcohol level. You are also considered as DWI if you have ingested any sort of controlled or chemical substance, including but not limited to prescription drugs, and they have impaired your thinking, your reaction time, and the like. When a person is stopped on suspicion of DWI, they are given tests to determine their blood alcohol and/or their drug levels. The legal limit of alcohol or drugs that can be in your blood is different for every state in the union. If the person who was stopped is under the age of 21, then those legal state limits are lower.