Human genetic variation has enormous implications for individual susceptibility to lung disease, as well as for differences in prognosis and response to therapeutic interventions. Single-nucleotide polymorphisms (SNPs) are the most common type of DNA sequence variation. An SNP is the substitution of a single base in the sequence for one that is different from that present in the majority of the population. In this review, we describe in more detail what SNPs are, how they are discovered, and their potential to elucidate the genetic basis of lung disease. We illustrate several examples of how SNPs are being used-or are poised for use-in diagnostic and therapeutic applications. We conclude with a brief discussion of the future of medicine and how genetic knowledge and application can play an ever-increasing and important role in more effective diagnosis and treatment at a more personalized level.