State certificates/licenses are typically issued at two levels. "Initial" licenses for new teachers are usually issued only once and are valid for about three years. Before an initial certificate/license expires, teachers must apply for a "standard" or "professional" certificate/license. These licenses for veteran teachers are valid for five years and must be renewed before the certificate/license expires.
If you do not apply for renewal within the proper time period, you must apply to have your license or certificate reinstated. To reinstate an expired license, you must typically complete a given number of college-credit courses and pass the state's subject area examinations for each subject area listed on the license. (In many states, you can apply for a "temporary" or "emergency" certificate/license and continue to teach while you complete reinstatement requirements; however, you will not meet No Child Left Behind "highly qualified" requirements if you hold a temporary or emergency certificate/license.)
Links to SREB State and Related Resources