Abstract: In this seminar, we discuss the distinction and possible equivalence between scale invariance and conformal invariance in relativistic quantum ?eld theories. Firstly, we give a brief review on the preceding works in relativistic quantum field theories in 2D, then we present the recent works on the same subject in 4D. The ultimate result of the discussion is: scale invariance plus unitarity implies conformal invariance in 4D. Our discussion is based on (arXiv:1107.3987, arXiv:1112.4538, arxiv:1309.2921 and arxiv:1309.4095).