Driving under the influence is illegal in every state. Generally, you can get a "per se" DUI for driving with a blood or breath alcohol concentration (BAC) of .08% or more. You can also be convicted of an "impairment" DUI if you drive while actually impaired by drugs or alcohol.
The consequences of driving under the influence are serious. Penalties for a first-offense DUI often include fines, license suspension, and substance abuse education courses. Some states also require mandatory jail time and ignition interlock devices (IIDs) for first DUIs. And even if you aren't ultimately convicted of a DUI in criminal court, the Department of Motor Vehicle might still take away your license if there's evidence that you drove with a BAC of .08% or greater.
Also, there are lots of costs of a first-offense DUI like attorney fees and insurance rate increases that can significantly increase the amount you'll actually end up paying.
What counts as a first DUI differs by state. Obviously, if it's the first time you've ever been convicted drunk driving, your current offense will count as a first DUI. But what if you have a prior DUI from a long time ago? Will the court treat your current DUI as a first—or a second—offense? It depends.
In some states, such as California, DUI convictions "wash out" after a certain number of years. For instance, in a state with a wash-out period of ten years, a 12-year-old prior wouldn't count: The court would treat your present offense as a first DUI. In states that don't have DUI wash-out periods, like Indiana, a second DUI counts as a second offense regardless of when the first happened.
The consequences and penalties of a first-offense DUI vary by state. Read specifically about the first-offense laws in your state.