Orthodox seed ageing, survival and longevity are discussed in relation to environmental factors during storage. It is explained why it has been necessary to introduce a new improved viability equation to quantify the relationship between seed longevity and storage environment. This new equation may be applied to predict the viability of seed lots of all cultivars of species after any period under a very wide range of storage environments. Other symptoms of seed deterioration which occur before death are discussed in terms of both the individual and the population. Evidence is presented for a model which represents and quantifies the development of ageing symptoms in seed lots.