Interstate 25 (abbreviated I-25) is an interstate highway in the western United States. Its odd number indicates that it is primarily a north-south highway. I-25 stretches from Interstate 10 at Las Cruces, New Mexico, to Interstate 90 in Buffalo, Wyoming.

The route is the main north-south highway through Colorado, passing through Cheyenne, Wyoming, near Fort Collins, Colorado, through Denver, Colorado, Castle Rock, Colorado, Colorado Springs, Colorado, Pueblo, Colorado, and over Raton Pass into New Mexico. The I-25 corridor in Colorado is heavily urbanized, passing just east of the Front Range of the Rocky Mountains. This stretch was recently involved in a massive renovation named T-REX (TRansportation EXpansion) in Denver, and COSMIX (Colorado Springs Metro Interstate Expansion). Major construction for T-REX ended August 22, 2006. COSMIX was completed in December of 2007. Several other smaller improvement projects for I-25 are still ongoing within Colorado.

I-25 map