There is a great deal of inconsistency and vagueness in the treatment of and terminology involved with software maintainability. This is exacerbated by the fact that there are a number of different dimensions of maintainability, each requiring specific treatment. The trends of increasing systems functionality and increasing systems complexity have given rise to new dimensions of maintainability since ISO/IEC defined maintainability as "the capability of the software to be modified" in 1996. This paper introduces the framework of maintainability and the techniques that promote maintainability in three abstraction levels; system, architecture and component. In the system dimension, the maintainability requirement is considered from a business-related point of view. In architecture, maintainability means a set of quality attributes, e.g. extensibility and flexibility. At the component level, maintainability focuses on modifiability, integrability and testability.