Proton is made up of quarks, antiquarks and gluons. We also know that proton has spin 1/2. How does the spin of the proton gets generated from different contributions from quarks and gluons ? What is the role of their orbital angular momentum ? These are intriguing questions in hadron physics. The answer seems to be not so straightforward, as the number of qaurks and gluons in the proton is not constant, it depends on the momentum or energy scale of the probe with which we investigate.