In this chapter we ascertain the significance of OLAP (On-line Analytical Processing) and its various tools useful for Accounting. We start with a brief history of OLAP. Then we define OLAP. We move on to analyze various types of OLAP- the Relational OLAP (ROLAP), the Multi-dimensional OLAP (MOLAP), the Hybrid OLAP (HOLAP) and the Desktop OLAP (DOLAP). We discuss some applications of OLAP tools in various areas of accounting. Finally, through a series of comparisons, we evaluate the different types of OLAP and select the type that could suit your needs.