Classification is everywhere. We classify birds and animals, languages and ethnic groups, stars, volcanoes, minerals and clouds, wine and blood, and colours and roses. We classify diseases, occupations and social status; the size of notepaper (grand eagle, elephant and pott); the dimensions of icebergs (small, bergy bits and growlers); and brandy (mellow, pale and superior).

It is natural to the human mind to classify, and essential if we want to make sense of the world, which is full of unique creatures and objects. Each day we encounter hundreds of these which we might never have seen before, but the process of classification allows us to recognize a street lamp, a dog, a magazine, a train, sandwiches for lunch, bananas, music on the radio, and make sense of those things. We don't need to investigate and learn about every new event in our lives because most of them conform to other objects and phenomena in our personal experience; we know what to expect of a dog or a banana, since they are similar to dogs and bananas we already know.

Everybody can and does classify, and if we spend so much time and energy classifying the world about us, it is natural to attempt to organize our stores of information about the world. It's necessary, too, to have systems for managing stored information in a way that allows us to find it again – systems that use our human classificatory skills to organize, to match, to predict and to interpret.

This is a book about some of the systems which people have created for organizing information. It also examines the problems we face in sorting out the relationships between subjects, and imposing order on chaos. It's about the nature of knowledge as it is found in books and other information-carrying media. It is also first and foremost a book about how to classify. The emphasis throughout is on the activity of classification rather than the theory, the practical problems of the organization of collections, and the needs of users.

You don't need any knowledge or experience of classification to use this book. It's intended for beginners, for students, and for people working in libraries who have never had any formal education or training in classification or subject cataloguing.