Measuring change is - or should be - a way of life for researchers the world over. Witness to events, we provide a means by which decision makers in business, politics, government and society in general can assess public opinion and evaluate the effect of change on that opinion. The most effective way to measure change in public knowledge and opinion is by the use of tracking studies. This paper uses four case studies to illustrate how tracking studies can aid decision making in communications generally and advertising specifically. The four case studies are: - "The EEC Referendum Campaign" - "Save Water" - "Simply Years Ahead" - "Ideas in Action". All four series of studies shared the similarity that results were needed to aid decision making for communication tactics, but differed significantly in their execution due to the subject matter and the differing time constraints imposed.