Magnetization processes of spin-1/2 Heisenberg ladders are studied usi
ng strong-coupling expansions, numerical diagonalization af finite sys
tems, and a bosonization approach. We find that the magnetization exhi
bits plateaux as a function of the applied field at certain rational f
ractions of the saturation value. Our main focus is on ladders with th
ree legs where plateaux with magnetization one third of the saturation
value are shown to exist.