Methodological implications of a person-oriented, holistic-interactionistic perspective in research on individual development are outlined, desirable properties of a mathematical model of a phenomenon are discussed, and selected methods for carrying out person-oriented research are briefly overviewed. These methods are: (1) the classificatory approach for approximately continuous variables; and (2) studying dynamical systems. The article also discusses issues that are important for the appropriate implementation of the person-oriented approach, including the match of problem and method and obtaining classifications using cluster analysis-based methods.