Step by Step Classification (SSC) is a formula-based library classification scheme. The classification number (CN) of a document can be derived based on a single formula CN = I date. Each letter I date is an element representing discipline, area, time, and extra information respectively covered in the text of the classifying document. Each element is prefixed to the respective class number which is useful in locating a document in the library. To provide classification numbers certain devices like NDA, CD, and LDD are provided. Hence all types of documents in any physical form can be classified. SSC allows for sufficient space to classify newly emerging disciplines which may be developed in the future. Language is not a barrier to classify documents; classification numbers can be allotted to any language with the help of NDA numbers. This formula will be useful for deriving computerized classification numbers. The same formula may also be used in other fields as mentioned in theory. This book describes the SSC in detail.