A formal group law is a formal power series behaving as if it were the product of a Lie group. In this talk, firstly we will mention some history and applications of the theory. Then we focus on formal group laws over a -algebra, guided by the principle that a formal group law is determined by its Lie algebra in this case. We will prove the -theorem,  i.e any -dimensional commutative formal group law over a -algebra is isomorphic to products of the formal additive group .