Olaru, G., Schroeders, U., Hartung, J., & Wilhelm, O. (in press). A tutorial on item and person sampling procedures in personality development research. European Journal of Personality. Abstract Measurement in personality development faces many psychometric problems. First, theory-based measurement models do not fit the empirical data in terms of traditional confirmatory factor analysis. Second, measurement invariance across age, which is necessary for a meaningful interpretation of age-associated personality differences, is rarely accomplished. Finally, continuous moderator variables, such as age, are often artificially categorized. This categorization leads to bias when interpreting differences in personality across age. In this tutorial, we introduce methods to remedy these problems. We illustrate how Ant Colony Optimization can be used to sample indicators that meet prespecified demands such as model fit. Further, we use Local Structural Equation Modeling to resample and weight subjects to study differences in the measurement model across age as a continuous moderator variable. We also provide a detailed illustration for both tools with the Neuroticism scale of the openly available 300-item IPIP-NEO inventory using data from the United Kingdom Sample (N = 15,827). Combined, both tools can remedy persistent problems in research on personality and its development. In addition to a step-by-step illustration, we provide commented syntax for both tools. Keywords: Ant Colony Optimization, Local Structural Equation Modeling, item sampling, person sampling, personality development The dataset used in this study can be downloaded at: https://osf.io/tbmh5/