This chapter focuses on the ontological component of platonism and surveys arguments for paradigmatic abstract entities. The debate between nominalists and platonists is inextricably connected with two ontological categories: abstract entity and concrete entity. This is because platonism asserts, while nominalism denies, that there are entities falling within the former ontological category. By distinguishing the ontological and categoreal components of platonism, isolating two kinds of disagreements that arise in connection with platonism. Despite the peculiar character of abstract entities, platonism is often claimed to be a commonsensical view well supported by the ordinary standards of judgment. Versions of platonism supported by the indispensability argument also inherit a second peculiarity concerning the scope of their commitment to mathematical entities. The argument from resemblance defends platonism by showing that the best explanation of the world's resemblance structure requires a commitment to abstract entities.