Sedentary plant-parasitic nematodes engage in a long-lasting and intimate relationship with their host plant. This interaction starts in the soil when freshly hatched infective juveniles are attracted to specific parts of a host plant root system. Little is known of what determines the attractiveness of host plant roots, but a mix of biochemical and structural cues from specific host tissues in the roots likely triggers invasive behavior in nematodes. Similarly to nematodes, phloem-feeding aphids and other piercing-sucking (hemipteran) insects must establish close associations with their host plants in order to modulate plant cellular processes to promote feeding and reproduction. This focus issue on molecular interactions between plants and different representatives of the animal kingdom sheds light on recent developments and offers a platform for exciting new data in this field. We are grateful to all the authors for their diverse contributions and for making this focus issue possible.