The last decade of research has revolutionized our understanding of respiratory microbiology, revealing that the lungs and airways contain diverse and dynamic microbial communities in health and disease. This "respiratory ecosystem"-a densely interconnected environment of microbial and host interactions-represents a tremendous and under-appreciated source of biological and clinical heterogeneity across patients with acute and chronic lung disease. Unlike other major sources of heterogeneity, such as comorbidities and host genetics, the respiratory microbiome is readily modifiable by clinical interventions, and therefore represents an untapped opportunity for therapeutic manipulation. As a potential "treatable trait" in efforts to subphenotype patients and deliver precision medicine, the respiratory microbiome is a promising therapeutic target. In this Pulmonary Perspective, we identify and discuss multiple challenges, both conceptual and practical, that must be overcome before the respiratory microbiome can be effectively modulated as a therapeutic target. Barriers include: 1) the need to identify specific microbiologic and ecologic "targets" for therapeutic modulation; 2) the need for an improved understanding of the efficacy and persistence of response to respiratory microbiome-modulating interventions; 3) the need for clinicians to be able to access, understand and utilize microbiome data for sub-phenotyping patients, and 4) specific concerns in special populations (including children, patients with chronic lung disease, and critically ill patients). By delineating these barriers, we identify opportunities for prospective research to advance our understanding of the respiratory microbiome, its role in human respiratory disease, and its genuine potential as a therapeutic target.