This award lecture reviews concepts of embryonic pattern formation developed since the time when, early in this century, insect embryogenesis first became a topic of causal research. These concepts, considered here in their historical sequence, are: (1) preformed patterns of determinants in “mosaic eggs”; (2) “regulative” pattern formation directed by a differentiation centre; (3) pattern specification by antagonistic polar gradients; and (4) the complex interactions of developmental genes recently revealed by genetical and molecular methods. These methods have triggered an epoch-making breakthrough in developmental biology, but they also can reveal surprising evolutionary aspects.