The formal group of an elliptic curve at a finite prime of the field of definition has proven to be a useful tool in studying the elliptic curve. Moreover, these formal groups are interesting in themselves. In this paper we define and study formal Drinfeld modules in a general setting. We also define the formal Drinfeld module associated to a Drinfeld module at a finite prime. The results are applied to the uniform boundedness conjecture for Drinfeld modules.
