The author of many science books for young people, among them Atoms Today and Tomorrow (1959, p. 873 J-267) and Plants Today and Tomorrow (1960, p. 50 J-18), now directs her audience's attention to molecules in action. Their activity, structure and special characteristics are described as they exist in solids, liquids and gases. Experiments in super-cold indicate their value to surgery. Special molecules have made possible the invention of synthetics and plastics. After an attentive tour of the field, the young scientist is invited to try his own hand at forming new molecules.