As per the course title, one of the most important aspects of functional programming that we shall cover is types. In this chapter, we shall describe what types are, how they are useful and how we can use type information to write code, and some aspects of types that allow us to reduce boilerplate code while still retaining type-safety. In addition, we describe how we can define our own data types in Haskell, and a neat feature known as pattern matching that is extremely useful in the presence of algebraic data types. We also offer some examples of how we can incorporate these concepts in Python.