Bacteriophages are probably the most abundant and diverse units in the biosphere. Phages are essential drivers for the dynamics of microbial communities since they influence the presence, abundance, and activity of bacteria both as lysogenic and as lytic phages. However, little is known about their impact, especially in areas that have been underexplored such as soils. With a combination of metagenomic analyses and cultivation-dependent approaches, my co-workers and I aim to gain insights into the genetic diversity and functions of phages to investigate their impact on bacterial diversity, virulence, bacterial evolution, and the stability of ecosystems. In collaboration with bioinformaticians, we analyze massive sequence data sets to resolve the "viral dark matter" and elucidate the ecological function of phages in the regulation of microbial abundances and diversity. The natural ability of phages to ultimately lyse their bacterial hosts also holds great potential for using phages biotechnologically or medicinally to eliminate harmful bacteria. In those days, antibiotics can no longer be the sole strategy for combating bacterial infections due to the steadily growing antibiotic resistance. Novel alternative strategies have to be developed, which might be synergistically applied in the future. Unexplored soil habitats represent a vast source for identifying new antimicrobials, i. a. phages against pathogenic bacteria in aqua- and agriculture and human pathogens. We frequently improve traditional cultivation techniques to enrich and isolate phages against pathogenic selection strains, e.g., Salmonella, Shigella, Vibrio, Klebsiella, Pseudomonas, Bacillus. These isolated phages are characterized concerning their structure, morphology, genome, host spectrum, stability, and resistance level for possible application. We further analyze the effectiveness and efficiency of phages on both planktonic and biofilm cells in vitro and in vivo. Moreover, we aim to improve the therapeutic potential of phages due to targeted genetic engineering of selected phages using modern molecular and synthetic biology methods. In one project, we combine two promising anti-biofilm strategies (Quorum sensing interference and phages) to attack pathogenic bacteria with genetically modified phages.