Given a family of smooth projective varieties $B$, the Hodge locus corresponding to a Hodge class $\gamma$ parametrizes all $b \in B$ where $\gamma$ remains a Hodge class. In this talk we discuss the definition of a Hodge class, variation of Hodge structures and the statement of the Hodge conjecture. We also look at the Lefschetz (1,1)-theorem which states that the Hodge conjecture is true in the case of divisors.