Competitive interactions shape the evolution of organisms. However, often it is not clear whether competition is the driving force behind the patterns observed. The recent use of experimental evolution in competitive environments can help establish such causality. Unfortunately, this literature is scattered, as competition for food, mates, and hosts are subject areas that belong to different research fields. Here, we group these bodies of literature, extract common processes and patterns concerning the role of competition in shaping evolutionary trajectories, and suggest perspectives stemming from an integrative view of competition across these research fields. This review reinstates the power of experimental evolution in addressing the evolutionary consequences of competition, but highlights potential pitfalls in the design of such experiments. What Does an Experimental Evolution Approach Add to the Study of Competition? Competition (see Glossary) has been extensively studied using mathematical models ever since the Lotka-Volterra equations [1]. Following these classical models, numerous ecological experiments were conducted in the laboratory [2-4] and in natural populations [5], providing many examples of both exclusion and coexistence between species or phenotypes competing for resources. Since then, competition has been studied in many contexts, and three main types of competition have been described (Box 1). Darwin identified competition as a source of evolutionary change [1]. In fact, one can argue that all evolution results from a competitive advantage of one genotype over another. However, there are specific questions pertaining to the role of competition, as an ecological interaction, on the evolution of populations. For instance, do traits improving competitive ability evolve, especially in the face of trade-offs with other life history traits [6,7]? How does competition drive niche width, that is, under which circumstances will individuals expand or contract the range of their resource use? When will character displacement evolve [8,9]? How do eco-evolutionary feedbacks, arising from how competition impacts the resource itself, change evolutionary responses? Unfortunately, study systems in which a causal link between competition and these evolved responses can be inferred are scarce [6,10,11]. Moreover, past competitive exclusion is nearly impossible to detect in the wild, a phenomenon coined as 'the ghost of competition past' [12]. Therefore, actual forces and mechanisms driving organisms' distributions and traits, and their impact on ecosystems, are difficult to assess retrospectively, hampering a complete understanding of the reciprocal effects of competition on evolution. Trends Organisms compete for several resource types, the most studied being food, mates, and hosts.