Aspect-oriented advice increases the number of places one must consider during reasoning, since advice may affect all method calls and field accesses. MAO, a new variant of AspectJ, demonstrates how to simplify reasoning by allowing programmers, if they choose, to declare limits on the control and heap effects of advice. Heap effects, such as assignment to object fields, are specified using concern domains--declared partitions of the heap. By declaring the concern domains affected by methods and advice, programmers can separate objects owned by the base program and by various aspects. When desired, programmers can also use such concern domain annotations to check that advice cannot interfere with the base program or with other aspects. Besides allowing programmers to declare how concerns interact in a program, concern domains also support a simple kind of semantic pointcut. These features make reasoning about control and heap effects easier.