This paper introduces some theoretical concepts based on optimality theory that may be applied to bat migration. Most predictions are based on flight mechanics and potential flight range. Optimal behavior will depend on the relevant immediate currency, such as safety, time, or energy. Predictions concern optimal flight speeds, stopover duration, fuel load at departure, and the adaptive use of winds. I also consider a criterion for fuel management when bats are migrating between summer and hibernation sites. The overall migration speed is predicted to be 46 km/day for a small (10-g) bat, and banding recoveries in Nathusius's bat (Pipistrellus nathusii) showed a mean speed of 47 km/day. The timing of migration in bats that minimizes the time spent in migration is considered a result of the trade-off between seasonally increased length of the night (decreased in spring) and reduction of aerial insect abundance. Most predictions remains to be tested; the theoretical framework herein offers a point of departure when designing new field or laboratory studies of bat migration.