Frontiers in Neural Circuits is a first-tier electronic journal devoted to understanding the emergent properties of neural circuits. The local circuits (microcircuits) constitute the elementary modules of the brain and interface between the cellular and systems levels of neural organization, while the global circuits (macrocircuits) connect the modules and brain regions to form the systems of the brain. The gigantic connectivity matrixes forming micro- and macrocircuits are still poorly understood, and the general rules by which these complex circuits operate are still a mystery. The major challenges are to understand the structural and functional architecture of these neural circuits and how their particular designs lead to the emergence of complex properties and behaviors. Articles revealing the microanatomy, physiology and pharmacology of any neural circuitry – ranging from retina, olfactory system, cerebellum, hippocampus, basal ganglia, all the way to neocortex – and covering species ranging from C. elegans to humans, are welcome. Our common thread is the study of the computational strategies used by different circuits, and, in particular, linking the function (either perceptual, motor, or internal) with the microcircuit structure. Submissions, which embrace and help explain the principles and importance of synaptic, cellular and connectivity diversity in neural microcircuits using multidisciplinary approaches are particularly encouraged. We also welcome studies with an evolutionary perspective to better understand how circuit design and capabilities changed to produce progressively more complex properties and behaviors. The journal also publishes research revealing how plasticity of circuits shapes the structural and functional architecture of neural microcircuits.