Neutrinoless double beta decay in 2025

Neutrinoless double-beta decay is currently the most sensitive known method for determining if neutrinos are Majorana particles. Significant progress over the past two decades in experimental techniques, background mitigation, and nuclear matrix element calculations has been coupled with negative results, implying potentially extremely long lifetimes. This review summarizes the process, recent theoretical and experimental advances, the challenges of increasing sensitivity to very long lifetimes, and promising future experimental efforts.