Interstate 355 (I-355), also known as the Veterans Memorial Tollway, is an Interstate Highway and tollway in the western and southwest suburbs of Chicago in the U.S. state of Illinois. Like most other toll roads in the northeastern portion of the state, I-355 is maintained by the Illinois State Toll Highway Authority (ISTHA). I-355 runs from I-80 in New Lenox north to I-290 in Itasca, a distance of 32.5 miles (52.3 km). With the exception of a four-mile (6.4 km) expansion in 2009, from U.S. Route 34 to 75th Street, the highway is six lanes wide for its entire length.

The Illinois State Toll Highway Authority (ISTHA) is an administrative agency of the U.S. state of Illinois charged with building, operating, and maintaining toll roads in the state. The roads, as well as the authority itself, are sometimes referred to as the Illinois Tollway. The system opened in 1958 in the Chicago area, and has subsequently expanded to include the eastern and central sections of Interstate 88 (I-88) extending into the northwestern part of the state. Beginning in 2005, the system was reconstructed to include more lanes and open road tolling, the latter of which uses I-Pass transponders to collect revenue as vehicles pass antennas at toll plazas or designated entrance or exit ramps. As of 2017, ISTHA maintains and operates 294 miles (473 km) of tollways in 12 counties in Northern Illinois.