Most birds cannot cover the distance between their breeding and winter quarters in one hop. They have to make multiple flights alternated with stopovers. Which factors govern the birds decisions to stop, to stop for how long, when to resume flight? What is better to accumulate much fuel and to make long flights for many hundreds of kilometres, or to travel in small steps? Is it necessary to find habitats similar to the breeding ones or other habitats would do? Are long migratory flights indeed so costly energetically as usually assumed? This monograph summarizes our current knowledge on the ecology of songbird migrants during migratory stopovers and on their behaviour.?