Icons are defined as signs which refer to their object by resemblance. However, the nature of the resemblance relation is controversial. In semiotics, the resemblance relation faces several problems, e.g. the problem of regression and the issue of symmetry (Sebeok 1979; 2001), which constitute a problem for iconic signs itself, putting into doubt the necessity of their existence as a separate class of signs (Bierman 1962; Dąmbska 1973, 1975; Eco 1976; Goodman 1968/76, 1972). There is no agreement on how to understand the concept of resemblance, either. Commonly, it is understood as a symmetric and reflexive relation. However, there are good reasons to consider it asymmetric and non-reflexive (e.g., Tversky 1977). Clarifying the nature of resemblance relation is not a definitional matter only. Understanding the nature of resemblance is crucial for understanding such fundamental mental capacities as categorization and pattern recognition (Sebeok 1979; Tversky 1977). Many theories and solutions to philosophical problems are based on the concept of similarity. For example, in psychology of perception, the ‘principle of similarity’ in the Gestalt tradition aims to explain how items sharing more features are more likely to be grouped together (Wagemans et al. 2012). Such theories are not complete without a solid foundation of a theory of resemblance.In our talk, we will briefly discuss the main approaches to defining the concept of resemblance in 20th-century philosophy and cognitive psychology. We will show that we lack a uniform understanding of the nature of resemblance and discuss possible solutions to this problem.