Mortality models used to assess longevity risk and retirement funding have been extended to stochastic models with trends and systematic risk. Systematic risk cannot be readily diversified in an insurance pool or pension fund. It is an important factor in assessing solvency and highlighting the tail risk in longevity insurance and pension products. Idiosyncratic risk can be diversified in typical pool sizes, although less effectively at the older ages. Mortality heterogeneity is not usually taken into account in stochastic mortality models. This is a mortality risk that reduces the effectiveness of idiosyncratic mortality risk pooling. Heterogeneity has been modeled with frailty models and more recently with Markov multiple state ageing models. This paper overviews recent developments in models for mortality heterogeneity and uses a model calibrated to both population mortality and health condition data to consider the impact of model risk and heterogeneity in assessing solvency and tail risk for longevity risk products.