Chapter 40B of the Massachusetts General Laws, known as the "anti-snob zoning" statute, was amended in 1969 to address a shortage of affordable housing in the Commonwealth. The law, commonly referred to as Chapter 40B, requires cities and towns to permit developers of affordable housing to apply to the local Zoning Board of Appeals for a "comprehensive permit" that covers all local approvals needed for development and supersedes applicable zoning. The statute established a Housing Appeals Committee to review any developer's appeal of local government denials, and of permits granted with conditions that threaten the viability of a proposed project. Chapter 40B, one of the first such laws in the country, was controversial when enacted, and has remained so. The law has been embraced by some developers and affordable housing advocates, but characterized as unfair by some towns who find themselves unable to appropriately prevent or control large developments in their community.

The law provides that in any community where less than 10 percent of the housing is affordable, developers can override local zoning rules in order to build residential projects that must include low and moderate income units. Chapter 40B was designed to encourage private rather than governmental development of affordable housing. “Affordable” is defined as housing that is affordable to and occupied by individuals and families whose annual income is less than 80 % of the area wide median income. More than 25,000 such units have been built since 1970. Between 1970 and 1999, zoning boards of appeals across Massachusetts granted 17% of the comprehensive permits applied for, and granted an additional 54% of such permits with conditions attached. During the same period, the Housing Appeals Committee upheld the local zoning board decision in 18 cases, overturned the local decision and ordered the granting of a comprehensive permit in 94 cases, and approved a compromise agreed upon by the developer and the local zoning board in 83 cases.

In order to be eligible for Chapter 40B, a development proposal must first be approved under a state or federal housing program. Either at least 25% of the units must be set aside solely for households that earn no more than 80% of the area median income, or at least 20% set aside for households below 50% of median income. Towns are allowed to establish a local preference for residents. Developers (whether for-profit or nonprofit) must also agree to restrict their profits.

Housing advocates say the law is crucial in Massachusetts, where real estate prices have sky rocketed. Existing and new construction in many suburbs has consisted of mostly expensive single-family houses on large lots. Those homes are not affordable for low-income families, including town employees who often can not afford to live in the towns in which they work. Many communities have far less than the statutory threshold of 10 percent affordable housing; some have less than one percent. Local government leaders, however, regard Chapter 40B as an inflexible and coercive regime that deprives them of control over development, largely denies them the ability to regulate new developments, and imposes a destructive or unsafe burden on municipal resources.

Suburban lawmakers have tried unsuccessfully over the years to weaken the law; various initiatives have sought to allow mobile homes to count towards the 10 percent affordability goal, to otherwise broaden the definition of affordable housing, or to lessen the mandatory nature of the process. In 2003, Governor Mitt Romney established a task force on Chapter 40B. That committee recommended preserving the law but amending it to soften its sometimes seemingly coercive nature by allowing towns to prevent multiple project proposals if they show progress toward increasing affordability within a year. Towns also get credit if they develop a plan showing how they will meet affordable housing goals over several years. The task force's recommendations were for the most part codified in regulations, but a permanent, statutory amendment failed in the legislature. Today, Chapter 40B itself remains unchanged from when it was first enacted thirty five years ago.

One of the primary objections to Chapter 40B is that many of the developments are large and unattractive, with extensive parking lots and little regard for environmental or traffic impacts. In 2004, in order to steer density towards town centers, the legislature passed Chapter 40R, which offers financial incentives to towns that change their zoning to create "smart growth" districts and to promote increased housing production in Massachusetts. "Smart growth" is a land development concept that emphasizes mixing land uses, and aims to increase the availability of affordable housing by creating a range of housing opportunities in neighborhoods. It promotes compact design, and preserves open space, farmland, natural beauty and critical environmental areas. The statute states that it "strengthens existing communities, provides a variety of transportation choices, makes development decisions predictable, fair and cost effective and encourages community and stakeholder collaboration in development decisions." When Chapter 40R residential complexes are built, the town gets $3,000 per unit from the state.

Chapter 40R requires affordability to be assured for a period of not less than 30 years through the use of an affordable housing restriction. The program is voluntary, and some commentators predict that very few if any towns will actually adopt such districts because the incentives are low relative to the control the towns have to relinquish to the state, and because the density requirements are too high for all but urban communities.

Indeed, only a few dozen communities have approved another voluntary program, known as the Community Preservation Act, to increase affordable housing. That Act, signed in to law by Governor Jane Swift in 2000, allows participating cities and towns to adopt a real estate tax surcharge of up to 3% to address three specific community concerns: creation and support of affordable housing, acquisition and preservation of open space, and acquisition and preservation of historic buildings and landscapes. A minimum of 10% of the annual revenues of the fund must be used for each of the three core community concerns. The remaining 70% can be allocated for any combination of the allowed uses, or for land for recreational use.

Commentators believe that the "density districts" of Chapter 40R are likely to be established, if at all, only by urban communities that have buildable land in downtown areas. If that prediction is correct, and the Community Preservation Act continues to be underutilized, then the "anti snob" zoning conflict will continue, with most suburbs offering limited affordable housing, and facing inevitable and protracted disputes over projects that take advantage of Chapter 40B.