  The integer quantized conductance of one-dimensional electron systems is a
well understood effect of quantum confinement. A number of fractionally
quantized plateaus are also commonly observed. They are attributed to many-body
effects, but their precise origin is still a matter of debate, having attracted
considerable interest over the past 15 years. This review reports on
experimental studies of fractionally quantized plateaus in semiconductor
quantum point contacts and quantum wires, focusing on the 0.7 x 2e^2/h
conductance anomaly, its analogs at higher conductances, and the zero bias peak
observed in the d.c. source-drain bias for conductances less than 2e^2/h.
