Graphene, a single layer of graphite, is a unique material characterized by Dirac quasiparticles with linear energy-momentum dispersion. The coupling of two graphene sheets in bilayer graphene leads to fundamental modifications of electronic properties. These systems have exhibited a spectrum of new physics as well as potentials for device applications. In this talk, I will present our recent investigations on monolayer and bilayer graphene employing infrared spectroscopy. In addition to a direct confirmation of Dirac quasiparticles in graphene, our study has revealed several new insights in these intriguing materials. I will discuss many body interactions in graphene, and the band structure of bilayer graphene.