Development and exacerbation of asthma have long been associated with exposure and sensitization to allergens. While exposure to respiratory allergens such as German cockroach, mouse, cat, and dust mite is thought to occur largely by inhalation, the best method to measure the exposure remains unclear. Similarly ambiguous are the ideal measurement and allergic or respiratory effects of exposure to fungi. As most people in the industrialized world, especially small children, spend the majority of their time indoors, the home environment is of prime importance. Previous researchers have shown that poor housing quality or maintenance lead to growth of fungi, increased pest populations, and higher concentrations of other allergens and irritants. These elevated levels in turn are associated with greater rates of sensitization and asthma in the occupants. This dissertation focused on exposure measurement, assessment of sensitization to common molds, and estimating the effects of neighborhood-level pest prevalence and housing quality on asthma symptoms. The study subjects and homes were part of either the Puerto Rican Asthma Study (PRAS), a longitudinal cohort study focused on identifying how multiple risk factors affected allergic sensitization and asthma development in U.S.-born Puerto Rican children with atopic mothers, or the Head Start Study (HSS), which examined allergen exposure and sensitization in young children of low-income families. From 199 of these New York City homes, settled dust, high-volume air, and nasal air sample measurements were simultaneously collected and analyzed for cockroach, mouse, dog, cat, rat, and mite allergens. Cockroach and mouse allergens were quantified from all three sample types while the other allergens were measured from air samples only. Ninety-three women from PRAS were tested for sensitization to six species of mold using the halogen immunoassay and four mold species using ImmunoCAP. The results were compared to previously quantified specific-IgE to other inhalant allergens as well as to self-reported allergy and asthma symptoms and demographic characteristics. Finally in a cross-sectional sample of 225 children from both study populations, the impacts of housing conditions and pests on current asthma at both the individual and neighborhood level were examined. Questionnaire data on demographics, housing factors, asthma symptoms, and health behaviors were evaluated with allergic sensitization and environmental sampling results for each child. They were also grouped and contrasted by neighborhood using United States Census neighborhood-level data on reported pest prevalence and housing quality. The effects of individual and neighborhood factors on current asthma symptoms were estimated using a generalized linear model. Allergen concentrations were generally highest in settled dust, followed by high-volumetric air, and then nasal air samples. Mouse allergen was most frequently detected in air samples, followed by dog, cat, and cockroach. No samples contained rat or any of three types of mite allergens above the detection limit. While all three measurements enhanced the exposure picture for mouse allergen, air samples rarely had detectable cockroach allergen despite being detected in settled dust. This led to the conclusion that settled dust sampling is still crucial when assessing a child's exposure to cockroach allergen but may be less important for buoyant mammalian allergens such as mouse. Nearly one-third of the 93 mothers were sensitized to one or more molds as determined by either assay. Being sensitized was positively associated with sensitization to tree, grass, or pigeon allergens but not to other inhalant allergens. Moreover there was no association seen between sensitization to the fungal species and asthma or allergy symptoms. Of note, however, interesting differences between the halogen immunoassay and ImmunoCAP were identified that merit additional investigation. For the 225 children, current asthma symptoms were positively associated with early respiratory infections, presence of environmental tobacco smoke, having higher concentrations of cockroach allergen in bed dust, a higher intensity sensitization level to one or more inhalant allergens, and current asthma in the mothers. After adjusting for individual-level factors (cockroach allergen in bed dust, environmental tobacco smoke, and study population), no effect of neighborhood-level characteristics could be associated with current asthma prevalence. The lack of effect was likely due to a combination of factors including: small sample size, self and other selection biases, and insufficient diversity across the study population and neighborhoods