The prime cause of the sorry “state of the art” in software development is our failure to produce good design documentation. Poor documentation is the cause of many errors and reduces efficiency in every phase of a software product’s development and use. Most software developers believe that “documentation” refers to a collection of wordy, unstructured, introductory descriptions, thousands of pages that nobody wanted to write and nobody trusts. In contrast, Engineers in more traditional disciplines think of precise blueprints, circuit diagrams, and mathematical specifications of component properties. Software developers do not know how to produce precise documents for software. Software developments also think that documentation is something written after the software has been developed. In other fields of Engineering much of the documentation is written before and during the development. It represents forethought not afterthought. Among the benefits of better documentation would be: easier reuse of old designs, better communication about requirements, more useful design reviews, easier integration of separately written modules, more effective code inspection, more effective testing, and more efficient corrections and improvements. This paper explains how to produce and use precise software documentation and illustrate the methods with several examples.