ABSTRACT
We begin this chapter by defining the lift of an orientation preserving homeomorphism. We then define the rotation number of a map in terms of its lift. We present some well-known examples that help making the notion of the lift of a map and its rotation number more clear. We then prove some properties of the rotation number of an orientation preserving homeomorphism. We finish this chapter by introducing Arnold tongues (the parameter values for which there is an attracting periodic orbit).
