As kids we used to collect a lot of objects like bottle tops, marbles, buttons, toys, pens and pencils, coins, books, etc. We also observe a flock of sheep or a herd of cattle grazing together, a class of students learning together, a basket of flowers, a bunch of keys and so on. In mathematics, such a collection of things or objects is called a set. Sets are valuable in understanding the properties of whole numbers and concepts of geometry. In fact sets help us to understand many topics of mathematics that would be difficult to understand. In this unit therefore, you will be introduced with the main concepts of sets and their types. Besides, you will learn about some relations among sets and basic set operations like union and intersection and their representations using Venn diagrams.