It is illegal to drive with a suspended or revoked license, without a license or with an expired license. Driving with an expired license means that your license was valid at some point, but you failed to renew it. Penalties for driving with an expired license vary by jurisdiction and often arise after you are pulled over for a traffic violation.
Most police officers have discretion over whether to issue a citation. For instance, one officer may let you off with a warning, whereas another will issue as many citations as possible. Penalties for driving with an expired license may include a ticket for $30 to over $250 (perhaps depending on how long your license has been expired), along with possibly getting detained and your car impounded.
If you are pulled over and receive a citation for an expired license, contact the court to find out if you can get your ticket dismissed by demonstrating that you have renewed your license. Sometimes, showing that you have remedied the situation is enough for a citation to be dismissed, though you may have to pay court costs or another nominal fine.