The book describes in great detail the complex life cycle of fleas based on the example of the cat flea ("Ctenocephalides" "felis"), the most important ectoparasite worldwide. Besides being the cause of painfully itching bites and allergic skin diseases, it is also a vector for viruses, bacteria, nematodes and cestodes. Over the years the market for insecticide use in small animals has become a major segment of the chemical-pharmaceutical industry.Insecticides of the new generation should not only fight the existing infestation (therapy) but should also effectively prevent new infestations for weeks (prophylaxis). The latest class of chemicals developed to this effect are chloronicotinyls (syn. neonicotinoides). Imidacloprid is the first member of this class of insecticides with a high selectivity towards the site of action within an insect. Applied to the skin it combats flea infestation persistently. The book describes the development of the compound from its discovery to its use in veterinary medicine.