At last year’s NDC, Scott Meyers devoted an entire day to guidelines for improving the quality of software, regardless of the application, the language in which it's written, the platform on which it runs, or the users it is intended to serve. This year, by popular demand, Scott isolates the single most important guideline from last year’s talk and focuses on it in this session. The guideline is Make interfaces easy to use correctly and hard to use incorrectly. Scott explains how this applies to both user interfaces and APIs, and, with specific advice and countless examples, shows how to employ it to improve the quality of the many interfaces in your software.