The purpose of this doctoral thesis is to contribute to the existing knowledge, that is, to expand the knowledge about consumer behavior in the market of eco-designed apparel and, based on the review of relevant literature and the author's research, to create an empirical model explaining the links between the considered variables. In addition to the stated primary objective, the dissertation seeks to explore the factors that may underlie human environmental behavior, then explore and critically analyze relevant theoretical and empirical insights into consumer behavior in the eco-designed apparel market, and examine the role of demographic variables (age and level of consumer education) as a moderator of the relationship between environmental issues and the intention to buy eco-friendly apparel. In addition to the pre-existing, custom variables of the Theory of Planned Behavior model (attitudes to buying eco-designed apparel, subjective norms, perceived behavioral control), factors included: health awareness, environmental concerns, knowledge of environmental issues, and cosmopolitanism. The empirical research for the purpose of the doctoral dissertation was conducted on a deliberate sample of 1194 respondents/consumers of the Republic of Croatia. According to the results of the primary research, in this doctoral dissertation an important role in predicting the intention to buy eco-designed apparel is: attitudes towards purchasing eco-designed apparel; health awareness; perceived knowledge of environmental issues and environmental concerns. The results of the primary study also found that the impact of perceived knowledge of environmental issues on the intention to buy eco-designed apparel is stronger among younger consumers, and that the relationship between buying eco-designed apparel and the intention to buy eco-designed apparel is greater among educated consumers than lower education level consumers.