Interstate 225 (I-225) is an auxiliary Interstate Highway in the U.S. state of Colorado. The freeway is a 11.959-mile-long (19.246 km) connector spur route of I-25 that acts as an eastern bypass in the Denver metropolitan area and serves Aurora. It also provides direct access to Denver International Airport for the Denver Tech Center and the southern suburbs of Denver. I-225 is one of the two existing auxiliary Interstate Highways in Colorado and it is the only auxiliary route of I-25, as there are no auxiliary routes for I-25 in New Mexico and Wyoming. The route begins at I-25 in the Denver Tech Center and runs north to I-70 north of Aurora. It interchanges with State Highway 83 (SH 83), SH 30 and I-70 Business/US 40/US 287, known locally as Colfax Avenue. The freeway was first proposed in the 1950s along with the first Interstate Highways within Denver. Construction did not begin until 1964 at the I-70 interchange and proceeded south through Aurora until final completion in early 1976 with the final link to I-25 opening to traffic.

In the US state of Colorado, Interstate 25 (I-25) follows the north–south corridor through Colorado Springs and Denver. The highway enters the state from the north near Carr and exits the state near Starkville. The highway also runs through the cities of Fort Collins, Broomfield, Loveland, and Pueblo. The route is concurrent with U.S. Route 87 (US 87), which is unsigned, through the entire length of the state. I-25 replaced US 87 and most of US 85 for through traffic.