There are more subtle conservation laws in particle physics like those of spin, baryon number[?] and more recently strangeness[?].
Noether's theorem expresses the equivalence which exists between conservation laws and the invariance of physical laws with respect to certain transformations (typically called "symmetries"). For instance, time-invariance[?] implies that energy is conserved, translation-invariance[?] implies that momentum is conserved, and rotation-invariance[?] implies that angular momentum is conserved.
Some conservation laws hold in many circumstances, but exceptions to them have been observed. Such is the violation of parity conservation; apparently the universe has "handedness" (right versus left).
In fact, quantities that are conserved, in some sense, seem to preserve what one would like to call some kind of a 'physical reality' and seem to have a more meaningful existence than many other physical quantities. These laws bring a great deal of simplicity into the structure of a physical theory. They are the ultimate basis for solving most physical variables.
wikipedia.org dumped 2003-03-17 with terodump