Ernst Haeckel (1834–1919) was a German biologist, naturalist, evolutionist, artist, philosopher, and physician who devoted his life to the research of flora and fauna, from the highest peaks to the deepest ocean depths. He was a fervent supporter and evolutionist of Darwin's theories, condemning the religious dogmatic view, writing philosophical treatises, earning a doctorate in zoology, and coining scientific terms that have come into everyday use, such as ecology, race, and stem cell. At the core of his colossal legacy was the desire not only to discover but also to explain. To this end, he created hundreds of detailed drawings, watercolors, and sketches of his findings, which he published in consecutive volumes, including collections of marine organisms and the imposing Kunstformen der Natur (Art Forms in Nature), which can be considered the basis of Haeckel's entire work. Like a curated visual encyclopedia of living organisms, Haeckel's work was as admirable for its graphic precision and meticulous shading as it was for the understanding of organic evolution. From bats to jellyfish, lizards to lichens, and spider legs to embryos, Haeckel identified the essential symmetries and order of nature, finding biological beauty even in the most unlikely organisms. In this book, the scientific, artistic, and environmental significance of Haeckel's work is celebrated with a collection of 300 of his best prints from some of his most important volumes, including Die Radiolarien, Monographie der Medusen, Die Kalkschwämme, and Kunstformen der Natur. In an era when biodiversity is increasingly threatened by human activities, the book is at once a visual masterpiece, an underwater exploration, and a vivid reminder of the precious diversity of life.