Various programming paradigms do exist out there. The two most widely known are Object Oriented Programming and Functional Programming.
Object Oriented Programming is and has been the most popular since the 1970s.
However, in the last two decades or so, Functional Programming having been generating waves and rising very fast.
In fact Object Oriented Programming Languages like Java, C# and Python have borrowed a wealth of features from Functional Programming Languages.
What most people don't know is that Object Oriented Programming paradigm is a like a child when compared to Functional Programming in terms of age.
In fact the oldest of the major programming paradigms(Object Oriented,Functional and Procedural) is Functional Programming(FP).
The very first well known functional programming language was the IPL, invented way back in 1955, even before Fortran(Procedural) which came one year later.
Functional Programming involves viewing programs as a collection of functions that accept arguments and return values.These functions are akin to mathematical functions and do not concern about the state of the program.
Instead of altering variables, newer values are returned so the variables never change.Functions make copy values and then change the copies while the original values remained ummutatated.
For iteration, recursion is used instead of loops.