The goal of this thesis dissertation is to address the question of whether there is heterogeneity within the human airway basal cell population and how we can answer the question experimentally. I will start by reviewing the physiology and cellular composition of the human respiratory system to highlight its complexity as it has two distinct regions, each with its own distinct morphology and cell types that dictate function. From there I will discuss the efforts of the Philip Streeter lab to generate and characterize novel monoclonal antibodies as molecular tools for the identification and isolation of cell subsets. During the course of my thesis research, we developed and experimentally validated a panel of monoclonal antibodies that allow us to study lung stem cell biology. After that I will discuss the historical development and current repertoire of in vitro assays that allow us to evaluate cell populations for stem cell function. Organoid assay systems are a useful tool for studying stem cells, especially in humans since in vivo assays are not available. Organoid assays are capable of assessing the stem cell properties of self-renewal and potency, or ability to differentiate. I adapted a bronchosphere assay to be able to assess stem cell function in uncultured, primary human airway epithelial cells. I will then discuss how the culmination of the monoclonal antibody characterization studies and the development of the bronchosphere assay allows me to identify a subset of airway basal cells that proves there is functional heterogeneity within the airway basal cell population. My novel HLO1-6H5 antibody identifies a subset of basal cells that is enriched for stem/progenitor cells. I will also discuss the results of additional preliminary studies that will provide an opportunity to advance the study of human airway stem cells and the molecular pathways that regulate their function. I will conclude my dissertation with a discussion of future research and translational opportunities for the HLO1-6H5 antibody and the novel cell subset that it identifies.