Philosophers often talk about and engage with ideas. Scientists, artists, and historians do, too. But what is an idea? In this paper, we first motivate the desire for an ontology of ideas before discussing what conditions a candidate ontology would have to satisfy to be minimally adequate. We then offer our own account of the ontology of ideas, and consider various strategies for specifying the underlying metaphysics of the account. We conclude with a discussion of potential future work to be (...) done on the ontology of ideas. (shrink)