This research will broaden the historical knowledge of Boston’s built environment by focusing on wood frame multi-family housing and its impact on Boston’s urban evolution. Although Boston’s historic core is primarily built of masonry construction, wood frame multi-family housing constitutes a vast majority of residential buildings in Boston’s peripheral neighborhoods built between the Civil War and the end of the nineteenth century. First, this research will identify and explicate the significance of wood frame multi-family housing to Boston’s social and urban patterns. Second, this research will document and analyze in drawings the architecture of wood frame multi-family housing in categories of three configuration types: row houses, three-family houses known as “triple-deckers,” and two-family houses. Third, this research will document in three-dimensional models the construction of wood frame multi-family housing in detail. The growth of industry in Boston and the influx of immigrants from Europe and rural America in the late nineteenth century forced the boundaries of urban development outward from the historic core to accommodate an expanding metropolis. The burgeoning streetcar system could transport the new city inhabitants out of the downtown core to Boston’s peripheral neighborhoods. These neighborhoods, called “streetcar suburbs” by Sam B. Warner, Jr., in his 1962 book of the same title, were the first ring of Boston’s outward development. New communities were rapidly constructed along the major transportation routes delineated by the radiating streetcar lines in a tightly-spaced pattern of free-standing wood frame houses. These neighborhoods became the place for the working class to escape the congestion, disease, and crime of the urban core. In 1920, Robert Woods and Albert Kennedy identified the expanding suburban ring as “the zone of emergence” in their book of the same title. Not only was this zone a place for the immigrant population to improve its living conditions, but also it was a place for this group to improve their economic and social standing by becoming property owners. The predominance of wood frame multi-family housing in the emerging suburbs is due to its relative low cost and its ease of construction. Although wood frame construction was labeled “balloon framing” due to its thin, membrane-like enclosure and lightweight structure, this new building technology revolutionized the construction of domestic architecture in Boston and across America. Mass-produced, standardized wood members could be assembled with a modicum of typical framing details and a minimum amount of skill making the knowledge of building accessible to all. To further simplify the production of this domestic architecture, a limited number of house-plan types were repeated consistently throughout Boston’s new suburbs. Wood frame construction democratized the building of domestic architecture by making its processes available to the commoner. This new building technology, combined with the streetcar, was the perfect engine for the rapid development of Boston’s zone of emergence. My research explicates the interrelationship between urban expansion, transportation, land-use patterns, and the construction of wood frame multi-family houses in Boston.