To mangle a paraphrase from John Donne, no mutant is an island — unless your mutant is an island. And even then it probably does not live entirely alone. Whether you are part of a community or a party of adventurers, Ancient philosophers from the Liver Pool had it right: everyone gets by with a little help from their friends. When two or more different species help each other, the cooperation is called mutualism. The coexistence may be symbiotic, where one creature lives on (or in) the other, like human gut flora; or it may be less intimate, like bees simultaneously feeding from flowers and pollinating them. In some cases, one species domesticates the other, like humans and dogs (or vice versa), while others just adapt their behavior to one another, like some large mammals standing lookout for each other at watering holes. The creatures in this issue illustrate varying degrees of this cooperative behavior, whether living in constant and necessary proximity, or just trailing along, one behind the other, hoping to snag a snack. They are listed as pairs or groups, making it easier to find creatures that operate together.