As a member of the Editorial Board who works in the field of invertebrate neuroscience, I feel very privileged by being able to introduce here the first thematic series of Neural Systems & Circuits [1]. Befitting the evolutionary history of neuronal circuits in the animal kingdom, this first thematic series will be entitled ‘Invertebrate Circuitry’. However, it is not only the evolutionary ‘seniority’ of invertebrates that justifies the dedication of this series to invertebrate neural systems and circuits. It is well known these days that work on invertebrate neurons and circuits has made a key contribution to our understanding of many fundamental processes governing the function of all nervous systems, including the human brain. These evolutionarily highly conserved processes include the ionic mechanisms of the membrane potential and action potential of nerve cells, the generation of receptor potentials, the one-way conduction of chemical synapses, the role of electrical synapses and the basic physiological mechanisms of the visual