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Maximal ideal

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In ring theory, a maximal ideal of a ring R is a proper ideal I\le R which is not contained in any other proper ideal of R. (That is, I\neq R, and there is no ideal J with I<J<R.)

One important property of maximal ideals is that if R is a commutative ring with unity then the quotient ring R/I is a field iff I is a maximal ideal of R.

From this it follows that in a commutative ring with unity that any maximal ideal is prime. Indeed if M is a maximal ideal of a commutative ring with unity R, then by the above observation R/M is a field. But then R/M must clearly be an integral domain, and this happens iff M is prime. Hence M is indeed a prime ideal of R.

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