Arizona State Route 101, or Loop 101, (spoken as one-oh-one) is a semi-beltway encompassing much of the Phoenix Metropolitan Area in the United States. It connects several suburbs of Phoenix, including Tolleson, Glendale, Peoria, Scottsdale, Mesa, Tempe, and Chandler. Construction began in the late-1980s and was completed in 2001. Additional general purpose lanes and a high occupancy vehicle lane (HOV) are being constructed along the eastern stretch of Loop 101 from Scottsdale to Chandler, starting at Princess Drive to Loop 202 (the Santan Freeway).

Loop 101 has interchanges with almost all area freeways, including: Loop 202, US 60, SR 51, Interstate 17, and Interstate 10 along its 61-mile (98 km) route.

Loop 101 begins as the Agua Fria Freeway west of Phoenix in Tolleson at a three-level interchange with Interstate 10. From that point, it heads north entering Phoenix then Glendale, passing the University of Phoenix Stadium and Jobing.com Arena. Continuing northward through Peoria, it passes the Peoria Sports Complex before entering northwestern Glendale and heading east just past the Arrowhead Towne Center mall. Loop 101 now heads eastward on the Beardsley Road alignment. The freeway enters northern Phoenix, and at milepost 23, Loop 101 intersects Interstate 17 near the Deer Valley Airport, 15 miles (24 km) north of Downtown Phoenix.

Continuing east as the Pima Freeway, it passes through the Union Hills area and then has an interchange with the northern terminus of SR 51 (Piestewa Freeway) at milepost 30. East of its junction with Route 51, Loop 101 curves south through Scottsdale in the northeast valley on the Pima Road alignment. The freeway curves east and continues onto the Salt River Pima-Maricopa Indian Community just south of Via Linda providing access to Downtown Scottsdale, a large open-air power center called Scottsdale Pavilions, Scottsdale Community College, the Salt River Pima-Maricopa Indian Community (and its two casinos), and Scottsdale Fashion Square. Continuing south, Loop 101 encounters an interchange with the Red Mountain Freeway portion of Loop 202 in Tempe at milepost 51, near the campus of Arizona State University. This interchange is partially built over the Salt River.

After this interchange, Loop 101 is now the Price Freeway, and interchanges with US 60 at milepost 55 before entering Chandler. Loop 101 provides access to Chandler Fashion Center just prior to concluding at milepost 61 at an interchange with the Santan Freeway portion of Loop 202.

An exit in Northeast Phoenix at 64th Street started construction in January 2008, and completed construction in the end of Q3 2008. Construction of Freeway Management System (FMS) for this segment of Loop 101. Using sensors, freeway cameras and the latest technology, the Valley’s Intelligent Transportation Systems keep traffic flowing by providing incident management personnel with information about real-time traffic conditions. Construction was completed on the segment between I-17 and State Route 51 in September 2009.

On August 26, 2010, comedian Robert Schimmel was involved in an accident on the road in Scottsdale in which his daughter was driving; their car flipped onto the side of the road. Schimmel died from his injuries on September 3, 2010.

The Arizona Department of Transportation is adding 30-miles of High Occupancy Vehicle (HOV) lanes on Loop 101 (Agua Fria Freeway) from Interstate 10 to State Route 51 (Piestewa Freeway). The project began in January 2011 and is set to be completed by the end of the year.

Also, three freeway bridges at 19th, 31st and 35th Avenues will be widened to accommodate the expanded freeway, two new overhead message signs will be installed and the northbound Bell Road off-ramp will be lengthened to ease congestion.

64th Street is planned to be a six-lane arterial and will be elevated approximately 30 feet above the existing ground over Loop 101. The interchange provides freeway access ramps (entry/exit) for both directions of Loop 101.

As of October 2012, the entire Loop 101 has one HOV lane in each direction, with direct HOV ramps to SR 51 and to Loop 202 Santan Freeway.

In 2006, Scottsdale installed speed enforcement cameras along its stretch of Loop 101 to combat the high fatality rate along its section of freeway. However, the speed enforcement cameras were discontinued in August 2006. They were restarted again in late February 2007.

The photo enforcement was based on inductive sheeting on the freeway bed located at six fixed positions along the freeway - three in each direction. The photo enforcement was in a trial phase, with the trial ending in December 2006. In January 2007, the program was authorized by Arizona Governor Janet Napolitano to resume in February 2007.

There has been much criticism of the program since its inception. For instance, in May 2006, a vehicle was allegedly clocked traveling at 147 MPH (237 km/h) on Loop 101. Scottsdale police arrested Lawrence Pargo soon afterwards. According to the manufacturer Hyundai, the vehicle the suspect was driving had a centrifugal governor, and was only capable of traveling 137 MPH (220 km/h).

The system is calibrated to ticket anyone traveling 76 MPH (122 km/h) or greater, as 65 MPH (105 km/h) is the predetermined speed limit. The system is also designed for night time use and utilizes equipment with a high intensity flash and full motion video capture to take pictures of fast-moving objects.

Money from a typical $162 ticket goes to the following:

Loop 101 has various names along its route:

The entire route is in Maricopa County.