Adaptation is considered to be a fundamental determinant of organismal evolution, but getting better at something may have an evolutionary cost. This limitation is encapsulated in the concept of a trade-off, where improvements in one trait come at the expense of another. For example, pathogens that excel at surviving in their host’s absence are often worse at causing disease, and vice versa. Knowledge of how trade-offs impact pathogens is particularly important as it would enhance our ability to predict disease emergence. However, while observations of trade-offs abound, we know little about why they occur. In order to gain crucial insight into pathogen evolution, I propose to investigate the underlying selective, environmental, and genetic constraints leading to life history trade-offs in Zymoseptoria tritici, an economically important pathogen of wheat in Europe with defined infection and survival stages. We will first determine the selective constraints on adaptation by contrasting the signatures of selection on genes expressed during survival, during infection, or both, across 15 global isolates. Then, by phenotyping a diverse panel of 150 Swiss isolates, we will identify infection-survival trade-offs, and test whether or not the strength and direction of trade-offs change in response to environmental conditions anticipated under future climate change. Finally, we will evaluate the importance of genetic constraints for shaping trade-offs by identifying loci contributing to both infection and survival (i.e., pleiotropy), and will furthermore determine whether or not the mechanisms of pleiotropy are related to carbon metabolism. Identifying the causes of trade-offs in a plant pathogen will not only produce broadly relevant insights into organismal biology and ecology, but will help European scientists exploit trade-offs to sustainably manage disease and bolster food security.