CARD9 is a member of the CARD protein family, which is defined by the presence of a characteristic caspase-associated recruitment domain (CARD). CARD is a protein interaction domain known to participate in activation or suppression of CARD containing members of the caspase family, and thus plays an important regulatory role in cell apoptosis.

This protein was identified by its selective association with the CARD domain of BCL10, a postive regulator of apoptosis and NF-kappaB activation, and is thought to function as a molecular scaffold for the assembly of a BCL10 signaling complex that activates NF-kappaB. Several alternatively spliced transcript variants have been observed, but their full-length nature is not clearly defined.