This review summarizes the present knowledge on the reproductive biology, mating system, sperm competition, sex allocation, and mating conflict in the simultaneously hermaphroditic land snail Arianta arbustorum (Linnaeus, 1758) (Helicidae). Field studies and controlled laboratory experiments indicate that mating is random with respect to shell size. However, subtle effects of inbreeding (reduced hatching success of eggs and viability of juveniles) and outbreeding were found. Individuals of A. arbustorum mate repeatedly with different partners and store viable sperm for more than one year. Spermatophore transfer is highly reciprocal, but the number of sperm they contain (800,000–4,000,000) is not necessarily equal. Snails need 3–4 weeks to replenish their autosperm reserves after a successful copulation. Sperm are monomorphic. However, there is considerable among-population—and to a minor extent—within-population variation in total sperm length. Sperm utilization patterns in double-mated individuals of A. arbustorum revealed striking differences among individuals. There is a huge variation in the structure of the spermatheca, which consists of 2–9 blind tubules. Different lines of evidence suggest that the snails might be able to store and expel sperm stored in single tubules and thus promote a selective fertilization of eggs (cryptic female choice). Maternal investment in eggs is considerable. Snails mated 1, 2, or 3 times showed that irrespective of the number of matings the individuals devoted >95% of the resources into the female function.