The route's current southern terminus is at the junction of I-95 and I-93 in Canton, and it is concurrent with I-95 around Boston for 37.5 miles (60.4 km) before it leaves the Interstate and continues on its own in a northeasterly direction towards Cape Ann.

Construction of the present circumferential highway began in Gloucester in the early 1950s and progressed southward, in part on new alignments and in part by the improvement of older roads, and came to completion with the final link into the Southeast Expressway (Route 3/John Fitzgerald Expressway/Pilgrim Highway) at a three-way flying junction known as the Braintree Split.

Subsequent upgrades on the northern segment in the 1960s completed a full freeway from Braintree in the south to Gloucester in the north.

It also approximately delimits the region served by the rapid transit and trolley system operated by the Massachusetts Bay Transportation Authority (MBTA).

At this present-day terminus, Route 128 runs concurrently with I-95, and follows the mileage-based exit numbering scheme used by I-95 as it enters Massachusetts from Pawtucket, Rhode Island.

The I-95 and I-93 signage were added in the mid-1970s when plans to construct I-95 through Boston, directly connecting the two I-95/Route 128 interchanges, were cancelled leaving a gap filled using Route 128.

An unused cloverleaf in Canton, partially removed circa 1977, was one of the leftover structures from this plan as well as the existing expressway (part of US 1 since 1989).

This decision caused a temporary reroute of US 3 onto the Yankee Division Highway, but in the opposite direction, to connect with its original route, one interchange to the north of the current junction, to become permanent.

This part of Route 128 was dubbed "America's Technology Highway", and signs marking it that way were put in place beginning in October 1982.

Two years later, those blue signs were changed to read "America's Technology Region" after complaints from veterans groups that noted the highway already had a name: the Yankee Division Highway,[4] a name bestowed in 1941 in honor of the U.S. Army unit first formed in Boston in 1917.

[6] As designated in 1927, the original Route 128, called the "Circumferential Highway", followed existing roadways from Gloucester to Hull through Boston's suburbs.

The final (southernmost) segment, originally built as the present eight-lane highway that spliced into the John Fitzgerald Expressway (then Route 3 for its entire length, and popularly also known as the Southeast Expressway) at a wye junction now known as the Braintree Split in Braintree.

This segment, which opened in 1960, replaced a two-lane undivided road to complete the first circumferential highway around any major city.

Concurrently, these agencies extended I-93 from its original terminus in Boston southward on the John Fitzgerald Expressway to the Braintree Split, then westward on the southern segment of the Yankee Division Highway to the junction with the completed southern segment of I-95 from Canton.

The Massachusetts Highway Department subsequently restored the designation of Route 128 and reinstalled signage on the segment of the Yankee Division Highway designated as I-95, partly in response to public protest and partly due to the fact that an Amtrak and MBTA commuter rail station adjacent to the highway at the University Avenue interchange in Canton bears the name Route 128 (RTE on the railroad timetables and in the Amtrak reservation system).

Despite no longer officially carrying the designation, the section of the Yankee Division Highway between Braintree and Canton is popularly called Route 128 within Massachusetts.

Much of this was along new alignment, but about half—mostly in Needham—was along existing roads: From Route 138 in Canton east through the Blue Hills Reservation in Canton, Milton, Quincy and Braintree, Norfolk County acquired right-of-way in 1927[12] and built the Blue Hill River Road.

[18] In 1955, Business Week ran an article titled "New England Highway Upsets Old Way of Life" and referred to Route 128 as "the Magic Semicircle".

The development of college-like suburban campuses and marketing to technology companies was intentional on the part of real estate developers such as Gerald W. Blakeley Jr.[20] In the 1980s, the area was often compared to California's Silicon Valley,[21][22] and the positive effects of this growth on the Massachusetts economy were dubbed the "Massachusetts Miracle".

By 1958, it became apparent that due to premature traffic congestion, the highway needed to be widened from four to six lanes, as business growth continued, often driven by technology out of Harvard University and MIT.

A $2.9 million federal stimulus project helped replace exit and highway signs in 2010 and 2011 along Route 128/I-95 from US 3 in Lexington to I-93 in Reading.

The southeastern freeway (Pilgrims Highway) that extends from Braintree to Cape Cod, Route 3, is also in the process of undergoing a similar "add-a-lane" project for much of its own 42-mile (68 km) length.

Construction on the sixth and final[26] segment in Needham and Wellesley began in January 2015, and included wider bridges and more auxiliary lanes and a new collector road.

[27] Major road construction ended in October 2018, and the project wrapped up with painting and landscaping in the spring of 2019.

[28] In 2015, the mayor of the City of Waltham, Jeannette McCarthy, noted that traffic was exceeding the capacity of Route 128 and proposed that communities located along the highway jointly consider a plan of establishing a form of monorail to add further mass transit options to businesses along the Route 128 corridor.

[34] In 2002, American mathematician Robert P. C. de Marrais named the routons, or the 128-dimensional hypercomplex numbers, after Route 128.