This paper centers on selected—and particularly, little recognized— problems in mammalian olfaction: (1) With certain exceptions the spacing of the external nares in most mammals does not favor orientation in an odor gradient by simultaneous comparisons of odor intensities (tropotaxis). (2) The mammalian nose is rich in both dynamic and static devices for conditioning and controlling the How of inspired air. (3) A well-developed vomeronasal organ is widely distributed but its function is obscure. (4) Nerve impulse traffic telemetered from the olfactory bulb of freely moving rats shows a varying pattern of discrete bursts of units with each inspiration and more sustained discharges. (5) Olfaction in species showing adaptations for lite in water, air, and underground is reviewed. (6) Because of its rich olfactory-trigeminal innervation the snout of pigs, moles, etc., may be considered as a “chemotactile” organ.