Most components and structures are submitted to load-time histories with variable amplitudes during their service life. Their safe design, in the context of weight reduction requirements, demands detailed and deep knowledge about the effects of spectrum shape, blocked or random sequences, material response, cumulative damage, residual stresses, environment and corrosion during lifetime in interaction with the variable load amplitudes. Especially, their reliability must be assured by appropriate testing, when test time reduction procedures are applied. Also, the substitution of variable amplitude loading by constant amplitudes is not generally possible because of the aforementioned influencing parameters and changed damage mechanisms. The proper consideration of effects of spectrum loading on lifetime requires that experiences in laboratory testing and service behaviour should be implemented in numerical assessment procedures.