In this presentation, we first introduce the classification of aggregation functions (conjunctive, disjunctive, averaging and mixed). For example, A: P^n -› P is a conjunctive aggregation function whenever, for all x from P^n, A(x) <= xi for all i from {1, . . . , n}. Then, some important classes of aggregation functions, including their history and some basic results, will be discussed. Finally, extensions of specific aggregation functions to act on bounded lattices will be given.