  We study localization in layered, three-dimensional conductors in strong
magnetic fields. We demonstrate the existence of three phases - insulator,
metal and quantized Hall conductor - in the two-dimensional parameter space
obtained by varying the Fermi energy and the interlayer coupling strength.
Transport in the quantized Hall conductor occurs via extended surface states.
These surface states constitute a subsystem at a novel critical point, which we
describe using a new, directed network model.
