My research uncovers patterns of parasite diversity and disease around the globe and investigates the underlying mechanisms that shape those patterns. Parasites have profound impacts on individuals, populations, and ecosystems, by affecting the transfer of energy through food webs, regulating populations, promoting evolution, and causing infectious disease. I primarily study parasites that infect commercially important shellfish and ecosystem engineers (e.g., seagrasses), whose loss would be devastating to an array of stakeholders. My research addresses three main questions: where are parasites, how are they moving around the world, and how do they cause harm? For the first question, I use genetic tools to determine distributional patterns and the many factors that influence them such as host specificity and environmental tolerance. For the second question, I focus on human-mediated dispersal of parasites, with ships as the primary vector in marine systems for the global dispersal and invasion of marine parasites. Finally, I use genomic tools to explore host-parasite interactions such as variations in disease virulence and pathogenicity.