Insects have extraordinary sensitivity to volatile odorants. In the case of pheromone reception, sensitivity approaches the single molecule detection limit. The mystery of how insects detect volatile odorants has intrigued researchers for more than a century, but only recently have the molecular underpinnings been uncovered. In this review we summarize recent work that reveals multiple signaling mechanisms utilizing several distinct receptor families underlie olfaction in Drosophila. Some of these mechanisms have not been observed in other animals, suggesting they evolved relatively late along an evolutionary branch that ultimately gave rise to the insects.