Walking a forest trail in Costa Rica, a visitor might be struck by the sight of an iridescent blue morpho butterfly fluttering ahead in the filtered daylight, or an enormous silk moth, as magnificently patterned and subtly coloured as a Persian carpet, only emerging to fly at night. Elsewhere, vivid yellow and orange sulphur butterflies flock to puddles to sip the concentrated minerals. Such is the dazzling variety of the butterflies and moths unique to this region. Gathered by biologists, Daniel Janzen and Winifred Hallwachs in the forests of north-western Costa Rica, 100 tropical butterflies and moths represent the diversity in large-format photographs by Jeffrey Miller that document the dizzying variety of shapes, colours, and markings. The photographs are accompanied by species accounts and images of the corresponding caterpillar. The authors recount these insects' feats of mimicry and migration, lift the veil on their courtship, and show how the new technology of DNA bar-coding is changing the picture of Lepidopteran biodiversity. The authors also tell the success story of Area de Conservacion Guanacaste, where the long-term work of Janzen and Hallwachs, a team of caterpillar collectors, and the participation of neighbouring farming communities has deepened understanding of Costa Rica's Lepidoptera and has brought about advances in restoration ecology of tropical habitats, biodiversity prospecting, biotechnology, and ecotourism development.