This book describes Classifier .It is a set of instances that have common features.classifier is a category of elements that have some common features, such as attributes or methods. classifier is an multiclass classification concept that serves as a mechanism to show classes and components.The development of expert systems has helped advance many fields by having computers reason more like humans.A classifier system is much more than a simple expert system that can learn from experience. classification is the problem of identifying to which of a set of categories a new population belongs, on the basis of a training set of data containing observations (or instances) whose category membership is known and testing sets through some parameters.In this book you understand about classification technique ,data sets,GP,Classifier,tree structure etc.