I am a plant biologist with a special passion for large organisms – trees! Trees are ‘large’ not merely by their physical or genome size, but primarily by their longevity. Longevity depends on a perennial growth habit, which can mean added functionalities for genes, proteins, and metabolites compared to herbaceous annuals. The quest for ‘what makes a tree a tree’ has led to various projects ranging from gene family evolution and functional diversification to transgenic manipulation of traits important to growth and development. We use a variety of experimental approaches in our investigations, ranging from transcriptomics, metabolomics, and CRISPR genome editing, to the more traditional tools of genetics, biochemistry and plant physiology. Needless to say, our research has industrial relevance due to the importance of forest trees as renewable feedstock. Our work is also of ecological relevance, because many of the traits we investigate are important in tree interactions with herbivores and pathogens.