Interstate 12 (abbreviated I-12) is an intrastate interstate highway located entirely within the state of Louisiana, United States. I-12 starts in Baton Rouge, Louisiana at Interstate 10, and travels along the North Shore of Lake Pontchartrain before ending at the intersection of Interstate 10 and Interstate 59 near Slidell, Louisiana[2]. In 1993, the state legislature renamed Interstate 12 as the "Republic of West Florida Parkway". In 2003, signs identifying the highway's official name and bearing the flag of the Republic of West Florida were erected by the Louisiana Department of Transportation and Development in order to highlight the unique history of Louisiana's Florida Parishes. I-12 is six lanes from its western terminus until Exit 7 (O'Neal Lane) at which point it becomes a 4 lane highway all the way to the eastern terminus.

The highway is relatively short for a mainline route at only 85 miles (138 km) - while Interstate 19 (63 mi. / 102 km), Interstate 66 (76 mi. / 123 km), Interstate 86 (west) (63 mi. / 101 km), Interstate 97 (18 mi. / 28 km) and the partially completed Interstate 99 (51 mi. / 82 km) are shorter, none of these have two termini with the same route, much less within the same state as well (I-99 will eventually extend into New York). Compare to the 73.5 mile (118 km) Interstate 295 in New Jersey and Delaware, which bypasses Interstate 95 or the 72.8 mile (117 km) Interstate 405 in California, which (arguably) bypasses Interstate 5.

I-12 map