SummaryThe development of multicellular organisms depends on correct establishment of symmetry both at the whole‐body scale and within individual tissues and organs. Setting up planes of symmetry must rely on communication between cells that are located at a distance from each other within the organism, presumably via mobile morphogenic signals. Although symmetry in nature has fascinated scientists for centuries, it is only now that molecular data to unravel mechanisms of symmetry establishment are beginning to emerge. As an example we describe the genetic and hormonal interactions leading to an unusual bilateral‐to‐radial symmetry transition of an organ in order to promote reproduction. Contents Summary 985 I. Introduction 985 II. Bilateral and radial symmetries 986 III. Symmetry breaking 987 IV. Symmetry transitions 988 V. Conclusions 989 Acknowledgements 989 References 989