Arabidopsis thaliana is now widely used as a model system in molecular and developmental biology, as well as in physiology and cell biology. However, ecologists and evolutionary biologists have turned their attention to the mouse ear cress only much more recently and almost reluctantly. The reason for this is the perception that A. thaliana is not particularly interesting ecologically and that it represents an oddity from an evolutionary standpoint. While there is some truth in both these attitudes, similar criticisms apply to other model systems such as the fruit fly Drosophila melanogaster, which has been extensively studied from an organismal perspective. Furthermore, the shortcomings of A. thaliana in terms of its restricted ecological niche are counterbalanced by the wealth of information on the molecular and developmental biology of this species, which makes possible to address evolutionary questions that can rarely be pursued in other species. This chapter reviews the history of the use of A. thaliana in organismal biology and discusses some of the recent work and future perspectives of research on a variety of field including life history evolution, phenotypic plasticity, natural selection and quantitative genetics. I suggest that the future of both molecular and especially organismal biology lies into expanding our knowledge from limited and idiosyncratic model systems to their phylogenetic neighborhood, which is bound to be more varied and biologically interesting.