<p>Programmed axon degeneration (PAxD) is an evolutionarily conserved mechanism in the nervous system that is activated by axonal injury (axotomy) to execute the self-destruction of a severed distal axon. It can also be triggered by non-axotomy insults, resulting in the loss of axons connected to their cell bodies. PAxD is therefore a promising target for therapeutic intervention and drugs that inhibit it are currently being tested in clinical trials. In this Review, we summarize the molecular mechanism of PAxD, focusing on its regulation by nicotinamide adenine dinucleotide (NAD⁺) metabolism and how it dictates Ca²⁺-mediated axonal demise. We examine its involvement in human disease and its potential as a therapeutic target by dissecting its role in various non-axotomy disease models. Finally, we address key challenges for its clinical translation, including the need for relevant biomarkers and safety considerations. Further advancements in understanding PAxD will pave the way for new therapeutic strategies targeting human axonopathies.</p>