This chapter introduces the definitions, concepts, theoretical paradigms, and approaches to social mobility research. From the time that Pitrim Sorokin wrote the first treatise on social mobility in 1927, the area of mobility studies in sociology has grown substantially. This has led, at times, to heated debates on the most appropriate way to measure and capture mobility. This chapter compares and contrasts the two key approaches to the study of mobility, that is, the status attainment approach and the class mobility approach. It focusses on gender, caste, and locality for the study of social mobility patterns in India and also provides a review of previous studies. The chapter ends with a thematic outline of the book as well as a discussion on the methods employed.