Pinning Down Patterns Professor John Hosking Director Centre for Software Innovation University of Auckland, New Zealand Design patterns are a very useful but somewhat elusive constructs. The more you attempt to formalise them the more they resist the formalisation process and the less the formalisms are useful for designers. This talk will cover some of the issues I have encountered in attempting to formalise design patterns through developing notational and tool support for them. I will review some of the approaches I and others have developed to attempt to resolve these issues but will also look at what I regard are more open problems in the area to stimulate debate.