Cystopteridaceae are a family of ferns in the eupolypods II clade of the order Polypodiales, class Polypodiopsida. They include four genera: Acystopteris, Cystoathyrium, Cystopteris, and Gymnocarpium. Gymnocarpium and Cystopteris have been found to be sister to the remaining Eupolypods II. Cystopteridaceae are small or medium-sized ferns in forests and crevices. They generally have thin laminae, and small, round, naked sori.