Stoats, weasels, martens and polecats belong to the mustelid family, along with badgers and otters, and feral American mink, which are a recent addition to the UK countryside, following escapes and releases from fur farms. This new volume in the New Naturalist Library focuses on the four ‘small mustelids’, all highly specialised predators, ubiquitous assassins to be marvelled at. There is a family likeness, the rather pointed snout, powerful jaws and sharp fangs and the long sinuous slender body with short legs. These small mustelids are also possessed of dense fur, which once led to their being hunted nearly to extinction. Some can kill prey larger than themselves, in some cases much larger, and they are uniquely adapted to hunt their rodent prey. They also have extraordinary lives – some in total seclusion, some in large, related groups – now brought into the light by one of the UK’s leading small mustelid experts.