Dealing with chiral fermions in gravity can prove a difficult task, which is not easily handled with Feynman diagrams. The path integral approach provides a powerful alternative, both on the formal and practical aspects. Recent improvements allowed to deal with chiral fermions in gravity, hence filling a gap in the literature. It then helped solving a controversy that spanned over a decade, concerning the presence or absence of the CP-odd Pontryagin density in the trace anomaly of the neutrino. In this talk, we describe how the path integral can be properly defined and used to compute quantum anomalies, and more generally we outline how it can be used to obtain a generic one-loop effective action for chiral fermions.