Functional programming emphasizes the use of pure functions, meaning functions that produce the same output for the same input without side effects. This programming paradigm promotes immutability and first-class functions, encouraging developers to build applications using functions as building blocks. Functional programming simplifies the reasoning about code behavior and enhances modularity, making it easier to maintain and test applications. Languages such as Haskell and Scala support this paradigm, aiming to produce clearer, more reliable code by emphasizing function application over conventional control structures.