Design patterns ease designing, understanding, and re-engineering software. Achieving a well-designed piece of software requires a deep nderstanding and a good practice of design patterns. Understanding existing software relies on the ability to identify architectural forms resulting of the implementation of design patterns. Maintaining software involves spotting places that can be improved by sing better design decisions, like those advocated by design patterns. Nevertheless, there is a lack of tools automatizing the use of design patterns to achieve well-designed pieces of software, to identify recurrent architectural forms, and to maintain software. In this paper, we present a set of tools and techniques to help OO software practitioners design, understand, and re-engineer a piece of software,sing design-patterns. A first prototype tool, PATTERNS- BOX, provides assistance in designing the architecture of a new piece of software, while a second prototype tool, PTIDEJ, identifies design patterns used in an existing one. These tools, in combination, support maintenance by highlighting defects in an existing design, and by suggesting and applying corrections based on widely-accepted design patterns solutions.