Since their colonisation of lands approximately 500 million years ago, insects have developed an astonishing variety of adaptations and have become the most diverse animal group on Earth. Insects are ubiquitous in terrestrial ecosystems. They maintain their function and support biodiversity by performing crucial ecological processes from pollination to decomposition. Unsurprisingly, writing a pocketbook of just over one hundred pages on insects is a monumental challenge that not every entomologist would comfortably take on. With his 60-year-long passion for insects, the late Simon Leather was arguably the best candidate for this task. Covering key aspects of insect biology and ecology, he managed to write a captivating book that can be enjoyed by professionals and the general public alike. With just nine chapters, Simon narrates an incredible story that starts with the evolution of insects from a crustacean ancestor from which the current 29 insect orders originated. Without overloading the reader with information, he explains the basics of insect biology and (mainly mating) behaviour. An additional chapter offers an overview of sociality, insect–plant associations, and symbiosis. When discussing terrestrial habitats, Simon explains how wings may have evolved, whereas he dedicates a separate chapter to the adaptations that allow insects to colonise freshwater habitats. I was not aware that Halobates species (Hemiptera: Gerridae) can be found in the open seas, and I have found the explanations about why insects have not successfully colonised the marine environment fascinating. Being passionate about butterflies, I enjoyed the chapter on defensive colourations, although other spectacular anti-predator strategies are missing. Since predation is not the only mortality factor, another chapter focuses on the adaptations of insects to survive extreme temperatures. One chapter highlights the many ecological roles of insects, including in agroecosystems, where insects are often considered beneficial or detrimental. Inevitably, the book ends by discussing the ongoing insect decline and accusing the unbalanced effort towards vertebrate research. Although colour photographs instead of black and white ones would have been better, this excellent primer can be recommended to all insect enthusiasts, particularly those who advocate the value of insects.