Conditions experienced early in life can have profound effects on phenotypes and subsequent life histories, and these effects can operate over different time scales and across generations in some cases. During early life, the environment can induce phenotypic effects which, while they may have short term benefits, can also carry long term costs. In this talk I will particularly concentrate on how variation in the plane of nutrition and in the level of stress exposure in early life can have long term consequences for fitness related parameters. This is based on experiments that we have carried out mainly in birds and fish, involving both field and laboratory based studies. I will also discuss a number of mechanisms that can underpin these effects, including changes to the reactivity to external stressors and to telomere dynamics, and discuss to what extent these induced changes might be adaptive. I will also briefly discuss the implications for conservation biology of these long lasting environmental effects on phenotypes.