Abstract: "In recent decades, geometric and mechanical insight into patterned cellular and tissue structures has increased considerably. With the recent development of experimental techniques, especially microscopy and other methods of cell imaging and tracking, phenomenological models can be tested and improved. Cell and developmental biologists are increasingly aware of the importance of these models; the idea that at the level of cells some morphogenetic processes and structures are be interpreted almost entirely by mechanical forces is more and more appreciated. This book covers a broad selection of biological tissues characterized by spatial order and regularity, from the checkerboard pattern of light and dark cells in the Japanese quail oviduct to the spherical shape of the shell-like sea urchin embryo. The patterns are interpreted using mechanical models based, for example, on the forces that make raindrops spherical or wrinkle the skin on our fingers in the bath. After reading this book, the reader will understand better why these patterns appear"