Composition mechanisms are intended to build a target system out of many independent units. The paper presents how the aspect technology may leverage the hierarchical composition, by supporting two orthogonal mechanisms (vertical and horizontal) for composing completely autonomous parts. The vertical mechanism is in charge of coordinating heterogeneous components, tools or services at a high level of abstraction, by hiding the technical details. The result of such a composition is called “domain” and, at its turn, it represents a high granularity unit of reuse. The horizontal mechanism composes domains at the level of their abstract concepts, even if they have been independently designed and implemented. The paper discusses the formalization of the vertical and horizontal compositions, and the wizard we have developed for generating the needed code (using Aspect Oriented Programming) in order to build the modeled applications.