Route 128, also known as the Yankee Division Highway (for the 26th Infantry Division), and originally the Circumferential Highway, is a partial beltway around Boston, Massachusetts, United States. The majority of the highway is built to freeway standards, and about 3/5 of it is part of the Interstate Highway System - all of which is along with Interstate 95. With the rapid growth of high-technology industry in the suburban areas along Route 128 from the 1960s to the 1980s, Route 128 came to symbolize the Boston high-tech community itself. However, today the industry has expanded significantly onto Interstate 495 as well, the next beltway out. In local culture, Route 128 is seen as something of a dividing line between the inner municipalities of Greater Boston and the more far-flung suburbs. The road's roughly 10-mile (16 km) radius, for example, also delimits most of the area accessible by the MBTA rapid transit system. Much of the area within Route 128 was developed before World War II, while the area outside it was developed more recently.

The south end of Route 128 is in Canton, where Interstate 95 heads south toward Providence, Rhode Island, just east of the Northeast Corridor's Route 128 Station. Common usage, as well as signs and official alternate designation until 1997, continues Route 128 east (signed south) along the first 7 miles (11 km) of Interstate 93 north to the Braintree Split in Braintree, where I-93 turns north with Route 3 toward downtown Boston. This section of former Route 128 serves as the north end of Route 24 to Fall River. (Until 1965, Route 128 continued further, southeast along Route 3 and roughly north on Route 228 to Hull.)

From Canton, Route 128 and Interstate 95 heads northwest, north, northeast and east around the Boston area to Peabody, where I-95 splits to head north toward Portsmouth, New Hampshire. Along this section, Route 128 has major interchanges with Interstate 90 (the Mass Pike), Route 2, U.S. Route 3, and Interstate 93. On roads approaching Route 128 here, guide signs only list I-95; Route 128 shields are in a separate sign assembly. U.S. Route 1 has also run along Route 128 near Dedham since 1989, forming a three-way wrong-way concurrency, with I-95 and Route 128 going one way and US 1 the other. (US 1 continues east on I-93 — former Route 128 — to Braintree, and turns north there with I-93 into Boston.)

After it splits from I-95 in Peabody, Route 128 continues east into Cape Ann. The freeway (termed a highway or expressway in Massachusetts) ends at a rotary with Route 127 in Gloucester, and the last bit of Route 128 is a surface road that bypasses downtown Gloucester to the northeast. After crossing Route 127 again (Route 127 runs in a loop through Gloucester and Rockport), Route 128 ends at Route 127A east of downtown Gloucester.

Despite a majority of Route 128's length running concurrent with either I-93 or I-95, many area residents refer to the entire length of the highway as Route 128. This includes the portion of I-93 south of Canton, which is no longer 128 at all, and substantial portions of I-95 that are not noticeably signed as 128. The perception of Route 128 running the entire length of highway from Gloucester to Braintree dates back to the road's pre-Interstate era, and has become an established part of local culture.

The route 128 number dates from the origin of the Massachusetts highway system in the 1920s. By the 1950s, it ran from Nantasket Beach in Hull to Gloucester. The first, 27-mile (43 km), section of the current limited-access highway from Braintree to Gloucester was opened in 1951. It was the first limited-access circumferential highway in the United States.

Route 128 runs concurrently with Interstate 95 from Canton north to Peabody and, when I-95 continues north from Peabody toward New Hampshire, east from Peabody to Gloucester. Until the early 1990s, it also ran concurrently with the present Interstate 93 from Canton to Braintree. This stretch of Interstate 93, which is now also designated as part of U.S. Route 1, though no longer officially part of Route 128, is still often referred to as "Route 128" by locals. 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. An unused cloverleaf in Canton, now removed, was the one leftover structure from this plan.

Until 1965, while and shortly after the Route 3 freeway to Cape Cod was fully finished, the section of current Route 3 between exits 15 and 20 was also designated as Route 128. The route's southern end was then truncated to its intersection with Route 3 in Braintree. The non-freeway section of Route 128 from Route 3 through Hingham to Nantasket was redesignated Route 228. The Massachusetts Highway Department has tried twice, in 1997 and 2003, to truncate 128 even further, back to its intersection with I-95 in Peabody, but local opposition has convinced them to back down. A reflection of these attempts are along every interchange, where the main signage on the intersecting route indicates the highway as I-95, while smaller signage to the sides also identifies the road as Route 128.

The area along the western part of Route 128 is home to a number of high-technology firms and corporations. This part of Route 128 has been dubbed "America's Technology Highway", and through to the end of the 1980s, was second only to Silicon Valley.

Route 128 makes more than a 180-degree arc around Boston, and clockwise is "north" even when the road heads slightly south of east when approaching the Atlantic Ocean. Hackers in the area refer to this as going "logical north" on the route. Interstate 93, going north-and-south, intersects Route 128, which nominally goes north-and-south, at a right angle, about 15 miles (24 km) north of Boston. A traveller going "logical south" on 128 (compass west) from the I-93 interchange will soon find himself driving due west, travelling logically south on 128 and I-95, and north on US 3 in a wrong-way concurrency.

Like the I-95 signage mapping onto 128, the mapping of US 3 onto this stretch of 128 is due to US 3 as a separate limited access highway terminating in Burlington on 128 instead of further south at Route 2 in Lexington as originally envisioned. This abrupt termination requires the US 3 signage to continue along 128 for somewhat over a mile until it can interchange the old US 3 surface arterial. Moreover, when I-93 and Route 128 ran concurrently south of Boston, before the route was truncated to the I-95 interchange in Canton, they were signed in opposite directions, so it was possible to travel north on I-93 and south on Route 128 at the same time.

Much of Route 128 is now part of the Interstate system, being concurrent with I-95 (and formerly I-93). However, the vast majority of locals will refer to these stretches as 128; it is uncommon for a local to use the Interstate designation(s) in ordinary conversation or while giving directions.

The northernmost several exits along Route 128, past exit 12, are not grade-separated interchanges. Exit 10 is signed as the signalized intersection with Route 127, and there are two rotaries between that and exit 12 (the Crafts Road interchange).

In the 1990s, the exit system was changed from concurrency along 128 to a system using the I-95 exits. The exits, which had gone from Gloucester to Braintree, were renumbered along I-95, from the Rhode Island state line to the border with New Hampshire. Exit 37 had been the interchange with I-93, which also had its exit numbered 37 at that interchange. Coincidentally, with the renumbering, exit 37 remained exit 37.

Route 128 Station is located along the highway in Westwood, Massachusetts and is served by Amtrak's Northeast Corridor line and MBTA commuter rail.

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". By 1958, it needed to be widened from six to eight lanes, and business growth continued. In 1957, there were 99 companies employing 17,000 workers along 128; in 1965, 574; in 1973, 1,212. In the 1980s, the positive effects of this growth on the Massachusetts economy were dubbed the "Massachusetts Miracle".

Major companies with locations in the broader Route 128 area included Digital Equipment Corporation, Data General, BBN Technologies, Thermo Fisher Scientific, Analog Devices, Computervision, Microsoft, GTE, Polaroid, Sun Microsystems, BEA Systems, Turbine, Inc., EMC Corporation, Autodesk, and Raytheon.

Route 128 was assigned by 1927 along local roads, running from Route 138 in Milton around the west side of Boston to Route 107 (Essex Street or Bridge Street) in Salem. Its route was as follows:

By 1928, it had been extended east to Quincy from its south end along the following streets, ending at the intersection of Route 3 and Route 3A (now Route 3A and Route 53):

The first section of the new Circumferential Highway, in no way the freeway that it is now, was the piece from Route 9 in Wellesley around the south side of Boston to Route 3 (now Route 53) in Hingham. Parts of this were built as new roads, but most of it was along existing roads that were improved to handle the traffic. In 1931, the Massachusetts Department of Public Works acquired a right-of-way from Route 138 in Canton through Westwood, Dedham and Needham to Route 9 in Wellesley. This was mostly 80 feet (24 m) wide, only shrinking to 70 feet (21 m) in Needham, in the area of Great Plain Avenue and the Needham Line. 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 a right-of-way in 1927 and built the Blue Hill River Road. This tied into West Street in northwest Braintree, which itself had been taken over by the county in 1923.

West Street led to Route 37, which ran southeast to Braintree center. This part of Route 37 had been taken over by the state in 1919 (to Braintree center) and 1917 (in Braintree center).

The rest of the new highway, from Route 37 east to Route 3 (now Route 53), through Braintree, Weymouth and Hingham, was taken over by the state in 1929. This was all along existing roads, except possibly the part of Park Avenue west of Route 18 in Weymouth.

By 1933, the whole Circumferential Highway had been completed, and, except for the piece from Route 9 in Wellesley south to Highland Avenue in Needham, was designated as Route 128. Former Route 128 along Highland Avenue into Needham center was left unnumbered (as was the Circumferential Highway north of Highland Avenue), but the rest of former Route 128, from Needham center east to Quincy, became part of Route 135. Thus the full route of the Circumferential Highway, as it existed by 1933, is now the following roads:

At the same time as Route 128 was extended along the new Circumferential Highway, it was extended further into Hull. This alignment, not part of the Circumferential Highway, ran southeast on Route 3 (now Route 53) (Whiting Street) to the border of Hingham and Norwell, where it turned north on present Route 228 (Main Street) through Hingham and into Hull. The exact route through Hingham was Main Street, Short Street, Leavitt Street, East Street, and Hull Street. The end of the numbered route was at the south end of Nantasket Beach, where Nantasket Avenue curves northwest to follow the shore of Massachusetts Bay.

The $315 Million MassDOT Highway Division Project has started widening on the project to upgrade the existing 14.3-mile (23.0 km) six-lane section of highway to eight lanes from north of Route 9 in Wellesley to Route 24 in Randolph. The project consists of adding a lane on the inside of each carriageway, complete with a 10-foot inside shoulder. The existing 1950s bridges, 22 in total, will be replaced as well. The project will be constructed in five phases over a twelve-year period. Construction of Phase 1 began in 2004. The first phase of the project consisted of replacing the existing three-lane Route 128 bridges over University Avenue/MBTA/Amtrak and the Neponset River with new four-lane bridges in Canton. The project also included construction of a new two-lane ramp from Route 128 to I-95. The $33 million project was awarded to SPS New England of Salisbury.

During the initial construction of Route 128, a provision had already been made for a fourth lane within the widely-spaced median along the 1.5 mile (2.5 km) length of Route 128 running from just north of the U.S. Route 1 interchange in Dedham, MA, north-westwards to the Route 109 interchange, and this will finally be used for the Add-A-Lane project.

Construction on Phase 1 was officially completed in October 2009. Construction of Phase 2 of the project began in summer 2006. This phase of the project consisted of the replacement of the Route 1 and Route 1A bridges over Route 128 in Dedham along with the road widening between Exits 13 and 15 (US 1). Construction of four sound barriers between the US 1 and I-95 interchanges were also included. This phase was completed in the Spring of 2011.

Construction on Phase 3, begun in April 2009, is widening I-93/US 1 to 4 lanes in each direction from Route 24 to the I-95 interchange. This phase of the project was expected to be completed by September 2011, however now will not be finished until mid-2012. Phase 4 of the Project, which began in March 2011, is replacing 7 bridges and widens Route 128 (I-95) to 4 lanes in each direction from Route 109 to south of Highland Avenue in Needham. This phase of the project is expected to be completed by June 2015 with an estimated cost of $88 Million, the most expensive contract so far. The southeastern freeway that extends from Braintree to Cape Cod, MA Route 3, is also in the process of undergoing a similar "add-a-lane" project for much of its own 42 mile length.

The Boston area MPO studied the Route 128/I-95 Corridor from approximately 2005–2010. The study focused on the heavily congested section from I-90 (Newton) to US 3 (Burlington), and was completed in November 2010. As of 2010, the highway carried over 200,000 vehicles per day. Some possible improvements to Route 128 include HOV Lanes, reconstruction of shoulders, ramp metering, bus on shoulder, and fiber optic traffic system improvements. More studies will need to be completed before projects will begin.

As of the end of 2011, the state is between resigning projects on Route 128 that are replacing the 25-year-old signs with new exit, regulatory and route signs. Starting in 1998 and continuing through 2002, signs were replaced through a $1.1 million project between Reading and Lynnfield. Progress continued in 2005 and 2006 during a $2.2 million project which replaced the signs on from Peabody to Gloucester, and continued with a $1.4 million project in 2008 and 2009 that replaced signs in Peabody and the remaining ones in Lynnfield. A $2.9 million federal stimulus project helped replace exit and highway signs in 2010 and 2011 along Route 128 from US-3 in Lexington to I-93 in Reading.

A project valued at $4.5 million is expected to begin in the Fall of 2012 that will replace exit & guide signs on Route 128 from Route 9 (Exit 20) in Wellesley to Routes 4/225 (Exit 31) in Lexington. And starting in Summer 2014 a new project is to replace a variety of signs from Highland Avenue in Needham to Route 109 in Dedham. New signage was put up between I-95 and US 1 in 2010 and most of the signage between I-95 and Route 24 has been replaced as of December 2011. New mileage markers were placed every 2/10 of a mile along the highway in 2010 (except for the area covered by the widening project) for I-93 between Braintree and Canton and I-95 from Canton to Peabody. New markers put along Route 128 from Peabody to Gloucester reflect the state highway's total mileage from Canton, indicating MassDOT's change of heart in decommissioning the route where it shares the road with I-95. The previous mile markers (reflected in the exit list below) had mile 0 in Peabody.

This exit list covers all of Route 128 as it existed before 1997. The stretch north of I-95, as well as the rest of the length before I-95 exit numbering was applied, has decreasing exit numbers traveling northbound (this is contrary to almost all highways in the US with numbered exits). Additionally, the lowest exit number on the highway is Exit 10 (which is an at-grade intersection near the highway's northern end). Route 128 is also the only highway in the state to contain directional exit designations (N/S or E/W after the number, as opposed to the traditional A/B/C in Massachusetts).

Route 128 currently has 18 numbered interchanges, starting at 29 (southbound) and continuing downwards to 10 (former Exit 27, an at-grade intersection, was removed, and there is no Exit 11).

Two songs by Massachusetts alternative rock artists, "Roadrunner" by The Modern Lovers and "Blue Thunder" by Galaxie 500, prominently feature Route 128 in their lyrics.