Many organisms such as bacteria, fungi, oomycetes, nematodes and insects grow, feed and/or reproduce in close association with plant hosts. To establish such intimate interactions, symbionts (either mutualistic or parasitic) secrete effectors into host tissues, which are molecules that modulate plant cell structures and processes (Win et al., 2012a). This last decade, advances in genomics have revealed that symbionts possess dozens to hundreds of effectors. Currently, the field is moving rapidly from effector identification towards effector characterization, which provides a better understanding of how these effectors promote the establishment of a successful relationship with host plants. The 30th New Phytologist Symposium clearly illustrated this theme, as an international panel of c. 150 scientists was brought together to discuss current efforts to decipher effector functions within a wide range of biological systems. The remote location of the meeting in the Sierra Nevada mountains of California, USA, promoted lively discussions between participants during and after the sessions, but also via social networks (the whole conference was covered by a twitter feed, #30NPS tag, available on http://storify.com/KamounLab/30th-new-phytologist-symposium-immunomodulation-by).