Dmix is an object-oriented environment for composing and performing music that is implemented in Smalltalk-80 (ParcPlace) on a Mac II. It attempts to provide the means to easily express musical ideas, to experiment with them, and to organize them into a musical composition. A major goal in its design was to enable composers to work with minimum interruption of the creative process---once a musical idea has formed it should be easy to find a way to implement it; during implementation the composer should not have to spend time writing code or consulting operating manuals. Dmix offers a rich variety of tools for creating, editing and modifying music objects. At any point the composer may choose to work via real-time editors, highly interactive graphic editors, hierarchy editors, text editors, applicative (functional) programming, or conventional alphanumeric programming in Smalltalk. All tools are equally available to the user at all times and may be used in any sequence and in conjunction with each other. Tools are easily extendable and can quickly be tailored to comply with specific needs. A unique feature in Dmix is the ability to create tools directly from music objects and vice versa. This enables composers to think of tools in more familiar musical terms that may help correlate between a desired musical effect and the means to produce it. This also offers alternative ways to deal with important musical concepts such as motivic treatment and development.