In these interviews, Erich Gamma, the famous Gang of Four (GoF) member and co-author of the landmark book, Design Patterns, talks about various design principles -

• In Part I: How to Use Design Patterns, Gamma describes gives his opinion on the appropriate ways to think about and use design patterns, and describes the difference between patterns libraries, such as GoF, and an Alexandrian pattern language.
• In Part II: Erich Gamma on Flexibility and Reuse, Gamma discusses the importance of reusability, the risks of speculating, and the problem of frameworkitis.
• In Part III: Design Priciples from Design Patterns, Gamma discusses two design principles highlighted in the GoF book: program to an interface, not an implementation, and favor object composition over class inheritance.

Hope you will find them useful.