The intestinal mucosa contains the largest population of antibody-secreting plasma cells in the body, and in humans several grams of secretory immunoglobulin A (SIgA) are released into the intestine each day. In the gut lumen, SIgA serves as a first-line barrier that protects the epithelium from pathogens and toxins. Recently, next-generation sequencing has revolutionized our understanding of the nature of the intestinal microbiota and has also shed new light on the important roles of SIgA in the regulation of host–commensal homeostasis. Here, I discuss pathways of IgA induction in the context of SIgA specificity and function.