Abstract: A ferrofin magnetic-fluid seal for hermetically sealing the space between a portion of a rotating member of magnetically permeable material and a portion of a close-fitting, spaced-apart stationary member also fabricated from magnetically permeable material and comprising a part of a housing for journalling the rotating member. The ferrofin magnetic-fluid seal is comprised of a plurality of concentric, fin-like projections of magnetically permeable material formed on each of the rotating member and the stationary member in spaced-apart opposing relation to define a plurality of magnetic gap regions. The magnetic ferrofluid is disposed within the magnetic gap regions. A magnetic field producing means is magnetically coupled in closed magnetic circuit relationship with at least the portions of the rotating and stationary members, the opposed fin-like projections and the magnetic ferrofluid trapped in the magnetic gaps defined between the opposing ends of the fin-like projections.