Emotions change over time. A comprehensive understanding of emotions will require that their temporal nature be observed and analysed. By observing emotion over time, one can disentangle and simultaneously analyse temporal variability within individuals and between-individual variability using a two-step process approach. First, within-person temporal patterns (e.g., covariation, lead–lag relation, periodicity, etc.) are assessed for each subject. Second, between-person analyses are conducted on the within-person patterns. These two steps can be done simultaneously with hierarchical linear models (HLM) or in two (...) actual steps with the process approach. HLM is limited to the intra-individual analysis of linear patterns (e.g., slope, intercept), whereas the process approach can be used to examine non-linear aspects of intra-individual change, such as multivariate patterns, within-subject skew, or phase relations between oscillating processes. In this paper we provide a description of the process approach and present several examples of, as well as suggestions for, intra-individual analysis applied to emotion and individual differences. (shrink)