  We propose the two formalisms for obtaining the noncommutative spacetime in a
magnetic field. One is the first-order formalism and the other is the
second-order formalism. Although the noncommutative spacetime is realized
manifestly in the first-order formalism, the second-order formalism would be
more useful for calculating the physical quantities in the noncommutative
geometry than the first-order one. Several interesting points for string theory
and fractional quantum Hall effect are discussed. In particular, we point out
that the noncommutative geometry is closely related to the fractional quantum
Hall effect(FQHE).
