Many serious illnesses are linked to everyday exposures to toxic chemicals. In the U.S., most chemical exposure comes from common consumer products such as pesticides, fragranced products, cleaning supplies, and building materials--products so widely used that people consider them "safe." As the links between everyday toxic exposures and potential health effects become better understood, evidence increasingly shows that reducing exposures can create a healthier society. Although some individuals may choose to build a healthy home and maintain a healthy household, they are still exposed to pollutants at their residences from the actions of others, such as to pesticides that are used by neighbors, businesses, and governments. They need healthy residential developments in environmentally healthy communities. This research investigates "healthy residential developments," defined as a property that aims to reduce pollutant exposures to the extent required by vulnerable populations, which for this research are individuals with multiple chemical sensitivities (MCS). Through a case study approach, this research investigates two exemplars of healthy residential developments, and explains how and why they form and continue. It also examines their implementation methods, and implications for planning and policy. Primary data collection methods included in-person interviews, telephone interviews, and site visits. Research strategies included the analysis of interview data, and categorical aggregation using thematic categories within and across cases. The categories focused on factors of formation and continuation for the two healthy residential developments. Findings include the challenges of people disabled with MCS to find safe housing; the importance of planning to address these challenges; the role of individuals, funding, and zoning in the formation of healthy residential developments; the role of funding, safe maintenance, and property management in their continuation; and, the need for affordable and safe housing for vulnerable populations. Future research can address the need to develop methods to create and sustain healthy residential developments, understand and reduce sources of exposure that initiate and trigger chemical sensitivity, and investigate experiences and implementation strategies in other countries.