An economy is best understood when we study its components or sectors. Sectoral classification can be done on the basis of several criteria. In this chapter, three types of classifications are discussed : primary / secondary / tertiary ; organised / unorganised ; and public / private. Another important issue highlighted is abut the problems caused by the changes in the roles of the sectors. The chapter has taken the example of unemployment and what the government can do to solve it. The declining importance of agriculture and growing importance of industry and services is been discussed.