Podospora anserina is a filamentous fungus used in manystudies of fundamental cell biology, including cell ageing. Inthis organism, ageing is defined as a diminution of cell abilityto proliferate and/or differentiate. This may or may notculminate with cell death. Two different ageing processes areintensively studiedThe `Senescence' phenomenon is present in all wild-type strains,results in cell death and is caused by a yet undefinedcytoplasmic and infectious element. It is associated withextensive mitochondrial DNA modifications. Longevity of thestrains is controlled by a highly complex network of genes. Amongthese, those involved in cytosolic translation and respiratorymetabolism are of special importance.The `Crippled Growth' phenomenon is present only in strains withelevated translational accuracy. It does not result in cell deathbut in a severe impairment of cell growth, an acceleration ofSenescence and a diminution of differentiation potencies. Nomitochondrial DNA modification is associated with CrippledGrowth. Another cytoplasmic and infectious element with peculiarproperties, C, is causally involved in the set up of this celldegeneration. The study of P. anserina degenerative processes provides aconceptual framework to understand ageing in more complexorganisms. Especially, it emphasises the complex control exertedby genes on longevity, the multiplicity of degenerative processesthat may occur to cells with identical genotype and the potentialrole of non-conventional infectious elements in cell ageing.