An inescapable consequence of sex in eukaryotes is the evolution of two sexes, generally are these males and females and two phases of the life cycle, a haploid and diploid phase. The existence of two sexes and two ploidy levels has important evolutionary consequences, which lie at the heart of our research. We aim to understand how selection acting at the diploid level affects the evolution of haploid gametes and in turn how selection at the haploid level affects the evolution of the diploid organism. We are particularly interested in the evolution of anisogamy and how postcopulatory sexual selection shapes the evolution of gametes, the evolution of different ploidy levels, the importance of sperm-mediated genetic and epigenetic effects and the evolution of sexual dimorphism and sex determination. We use a multitude of study organisms including the zebrafish Danio rerio, the Atlantic salmon Salmo salar, the filamentous fungus Neurospora crassa and the fission yeast Schizosaccharomyces pombe and combine different approaches such as comparative methods, experimental evolution and selection experiments, mathematical modeling, genetics and genomics.