This report contains the most comprehensive assessment of the status and trends of the world’s invertebrates conducted to date. It introduces the staggering diversity of invertebrates, ranging from microscopic zooplankton to giant squid. Together these organisms represent around 80% of the known species on our planet. They not only provide a bewilderingly rich and varied component of the natural world, they are our natural capital; the engineers of the many benefits which humans accrue from an intact and fully functioning environment. This report documents several reasons for concern about the health of invertebrates. The conservation attention paid to invertebrates to-date lags far behind that of vertebrates (mammals, birds, reptiles, amphibians and fish). If their path follows that of many of the high profi le vertebrate species, our world would not only be depauperate in the organisms that give it life, but we would compromise the many benefits that humans gain from our environment.