In this tutorial, we will take a look at polymorphism, the virtual and the override keywords in C#. Polymorphism is one of the main concepts of OOP(object-oriented programming). It means that child classes can be viewed as parent classes at run time. Suppose we have a method that takes a parent class as an input. We can pass it the derived class and everything will still work. This can work because the child method inherits the required members from the parent class.