Filter-feeding in marine invertebrates is a big and important research subject, which cannot be even approximately covered by the present six articles. But although these articles deal with a limited and rather random selection of both topics and filter-feeding species, they give an update of certain aspects of important ongoing research. The articles deal with many topics, such as: filtration rates, energy budgets, growth rates, bioenergetic modeling, filter-pump design, particle-capture mechanisms, functional morphology, and hydrodynamics studied in sponges, jellyfish, mussels, and other filter-feeding marine invertebrates. This makes the Special Issue relevant for all marine biologists.