Green consumerism and the role of eco-marketing have become increasingly important for increasing the market share of sustainable (non-) food products. The current study examines the effect of social identification with certain green consumer groups on brand knowledge, brand attitude and buying behavior. An online panel study was conducted among a representative sample of the German population (N=961). For brand knowledge and brand attitude, we presented five well-known organic brands in the German market to the respondents. To test the hypothesized model, we used structural equation analysis in SPSS Amos 16.0. Several competing path models were tested. One of the main conclusions of the current study is that people who are aware of their social identity concerning environmentally friendly consumer groups also seem to feel more attached to consumers who buy organic food products. In addition, brand knowledge and brand attitudes concerning specific organic brands have an effect on buying behaviors for organic food products. Moreover, the influence of brand knowledge on buying behavior seems to be mediated by brand attitude. The results of the current study can be used to develop more effective branding strategies in eco-marketing. Aside from classical strategies, marketers could use social identity theory to create future market strategies with regard to green consumerism.