The cystic fibrosis airways harbor complex and dynamic microbial communities whose interactions with one another and the host are thought to be major players in pulmonary decline. However, details of their in situ physiology are lacking relative to their behavior on the lab bench. This seminar will focus on two vignettes that address the spatial and temporal in situ dynamics of CF lung microbiota. The first describes a metabolic labeling approach that, when coupled with fluorescent imaging, flow cytometry and genomic approaches, can differentiate actively growing cells from those that are dormant/dead and reveal their taxonomic identities. The second will focus on the role of mucins as a nutrient source for pathogen growth in the lower airways. Specifically, we have revealed a potential role for oral-derived anaerobic bacteria, most commonly thought of as “commensal” flora, in the degradation of respiratory mucins. Mucin-derived metabolites generated through this process can then stimulate the growth and pathogenicity of Pseudomonas aeruginosa and other canonical lung pathogens. This cross-feeding relationship will be discussed in the context of lung disease establishment and progression, and its implications for medical management.