Atypical T cells take a different path Conventional T cells recognize peptides that are presented by polymorphic major histocompatibility complexes (MHCs). By contrast, many tissue-resident T cells, such as mucosal-associated invariant T cells, invariant natural killer T cells, and γδ T cells, respond to modified peptides and small molecules presented by conserved MHC-like molecules. Unconventional T cells are important for host defense and tissue repair and seed tissues during critical early-life windows of development. Constantinides and Belkaid review recent advances describing how unconventional T cell subsets compete for early-life signals, including those from the microbiota, which instruct their development and have enduring consequences for the health of the host. —STS