Vertex operator algebras (VOAs) and their modules define sheaves of conformal blocks over the moduli space of stable curves, generalizing sheaves of conformal blocks attached to Lie algebras. In this talk I will discuss how these sheaves are constructed and which properties they satisfy. I will in particular describe conditions that guarantee that these sheaves are actually vector bundles of finite rank and related open questions. This is based on a joint work with A. Gibney, N. Tarasca and D. Krashen.