We begin the chapter with analytic continuation which is a process to extend the domain of definition of analytic function in which it is originally defined. Usually, the domain of definition of analytic function depends upon how it has been defined. For example, for every power series, there is an analytic function inside the circle of convergence. Here, we will also establish the fact that there exists an analytic function which coincides with power series representation interior to the circle of convergence. In Section 9.4, we deal with infinite product which has close analogy with infinite series concerning convergence of different types. At the end of the chapter, we will discuss Dirichlet problem which ...