Human cognition and behavior are not uniform and have wide variations, namely individual differences-the (psychological) characteristics that distinguish one person from another and help define their individuality.As I write this editorial, the COVID-19 pandemic continues to tragically affect societies worldwide; unfortunately, while some patients are more prone to severe illnesses, others are not.This phenomenon may be considered dependent on individual differences.Recent research has also found a broad range of individual differences in the amounts of SARS-CoV-2 antibodies in convalescent individuals (Robbiani et al., 2020).Thus, individual differences cannot be ignored in scientific research.Cronbach (1957) distinguished between two streams of psychological science: experimental and individual (correlational).In the former, individual differences are simply regarded as measurement errors, whereas the latter attempts to capture working implications for individual differences, expressing them as functions of personal characteristics.Despite the diverse ways of thinking about individual differences in psychological science, one cannot deny that we can only highlight individual characteristics more clearly when we adopt multiple perspectives in evaluating individual differences rather than look at them from a single standpoint.Scientific attitudes toward individual differences depend on how we view and understand the nature and characteristics related to individual differences.Therefore, we need to properly examine the situations in which individual differences exist, either generally or domain-specifically, and how they are developed.This special issue aims to showcase state-of-the-art individual difference research.The first article by Wakabayashi (2020) tested the usefulness of the five-factor model (FFM) of personality traits, known as the Big Five, in the categorical diagnosis of personality disorders.The results demonstrated that the FFM of personality traits only partially predicted personality disorders, suggesting that the model may not be appropriate in capturing both personality trait description in the normal range and categorical personality disorder diagnosis on the same axis.The FFM of personality traits is sometimes treated as the only solution when depicting individual differences in personality traits.However, this study caused some controversy with that idea and provided empirical evidence that the FFM is not panacea for personality research.