Bacteriophages, like all viruses, display remarkable diversity in the type and size of their genetic material, as well as in the structure and dimensions of their virus particles. However, much of this diversity remains unexplored due to the vast, almost unimaginable number of phages in our biosphere.Omics approaches have provided valuable insights into this diversity but often lack direct links to function. Uncovering such connections through isolate-based research can offer deeper understanding of how phage–bacterium interactions shape natural ecosystems, while also paving the way for new tools in molecular biology and phage-based applications. In this talk, I will present how environmental phages, especially those originating from boreal freshwaters, are advancing our understanding of phage biology and phage–host interactions. I will highlight examples ranging from phages with some of the smallest to those with the largest known genomes, including the first cultivated megaphages.