All natural populations are constantly subject to new mutations, and frequently face new environments, to which they adapt. Knowledge of the genetics of adaptation should provide the centerpiece of a unified theory of evolution. Despite its extreme importance, the process of adaptation is far from being understood. How does the shape of distribution of fitness effects of mutations depend on the environment? What is the importance of epistasis in adaptive evolution? are still open questions. While empirical observations on advantageous mutations are extremely difficult, recent technical advances allow us to start tackling these questions with an unprecedented accuracy. Here we will combine different methods in a novel powerful marker system to track adaptive mutations as they become incorporated into bacterial populations adapting to different environments and as they fix. Interestingly theory suggest that some generalities may underlie the process of adaptation and that ecology may be important in the dynamics and statistical laws of adaptation. Experimental evolution with bacteria presents us with the opportunity to directly measure key parameters and to test theoretical predictions about the genetic basis of adaptive evolution in increasingly complex ecosystems. As Dobzansky pointed out The greater the diversity of inhabitants in a territory, the more adaptive opportunities exist in it. The main goal of this research project is to measure rates and effects of adaptive mutations, as well as patterns of epistasis amongst beneficial mutations in environments with different strengths of abiotic versus biotic interactions.