ABSTRACTTransfer RNA (tRNA) modifications play an important role in regulating mRNA translation at the codon level. tRNA modifications can influence codon selection and optimality, thus shifting translation toward specific sets of mRNAs in a dynamic manner. Queuosine (Q) is a tRNA modification occurring at the wobble position. In eukaryotes, queuosine is synthesized by the tRNA‐guanine trans‐glycosylase (TGT) complex, which incorporates the nucleobase queuine (or Qbase) into guanine of the GUN anticodons. Queuine is sourced from gut bacteria and dietary intake. Q was recently shown to be critical for cellular responses to oxidative and mitochondrial stresses, as well as its potential role in neurodegenerative diseases and brain health. These unique features of Q provide an interesting insight into the regulation of mRNA translation by gut bacteria, and the potential health implications. In this review, Q biology is examined in the light of recent literature and nearly 4 decades of research. Q's role in neuropsychiatric diseases and cancer is highlighted and discussed. Given the recent interest in Q, and the new findings, more research is needed to fully comprehend its biological function and disease relevance, especially in neurobiology.