We breathe roughly half a billion times in a lifetime, generally in an effortless and even unconscious manner owing to activity of a respiratory central pattern generator (CPG) located in the hindbrain. The respiratory CPG relies on the coupling of two prominent rhythmogenic sites located in the medulla, the pre-Bötzinger Complex (preBötC) and the para-Facial Respiratory Group (pFRG). Working in the mouse embryo, we have identified the emergence of forerunning versions of these two oscillators using developmental genetics tools, electrophysiological and optical recordings. We have defined molecular and functional signatures for cells destined to form each oscillator. More precisely, we have shown the independent development of (i) an Egr2- (also known as Krox20-) derived, Phox2b/Lbx1/Atoh1-expressing embryonic parafacial oscillator and (ii) a Dbx1-derived population of glutamatergic interneurons required for both preBötC rhythm generation and bilateral synchrony. These results indicate that each oscillator is not assembled from cells of disparate origins. Rather, each oscillator is made of cells featuring selective built-in functional properties that derive from a discrete transcriptionally defined domain of the neuroepithelium. Hence, the dual organisation of the respiratory CPG seems to reflect the modular origin of its composing cells.