One challenge facing research on personality development over the lifespan is how to differentiate developmental effects (i.e., changes in individuals over time) from age differences (e.g., older people having higher average trait levels than younger people). This talk will present two approaches to tackling this issue: multilevel models and local structural equation modeling (LSEM). In multilevel models, age can be included as a Level-2 predictor to disentangle the effects of age and time. In LSEM, the parameters of interest, such as those from a latent change model, are estimated conditional on age to achieve the same goal. Both methods will be illustrated using empirical data from large samples on the development of the personality trait narcissism.