  Spontaneous synchronization is a general phenomenon in which a large
population of coupled oscillators of diverse natural frequencies self-organize
to operate in unison. The phenomenon occurs in physical and biological systems
over a wide range of spatial and temporal scales, e.g., in electrochemical and
electronic oscillators, Josephson junctions, laser arrays, animal flocking,
pedestrians on footbridges, audience clapping, etc. Besides the obvious
necessity of the synchronous firings of cardiac cells to keep the heart
beating, synchrony is desired in many man-made systems such as parallel
computing, electrical power-grids. On the contrary, synchrony could also be
hazardous, e.g., in neurons, leading to impaired brain function in Parkinson's
disease and epilepsy. Due to this wide range of applications, collective
synchrony in networks of oscillators has attracted the attention of physicists,
applied mathematicians and researchers from many other fields. An essential
aspect of synchronizing systems is that long-range order naturally appear in
these systems, which questions the fact whether long-range interactions may be
particular suitable to synchronization. In this context, it is interesting to
remind that long-range interacting system required several adaptations from
statistical mechanics \`a la Gibbs Boltzmann, in order to deal with the
peculiarities of these systems: negative specific heat, breaking of ergodicity
or lack of extensivity. As for synchrony, it is still lacking a theoretical
framework to use the tools from statistical mechanics. The present issue
presents a collection of exciting recent theoretical developments in the field
of synchronization and long-range interactions, in order to highlight the
mutual progresses of these twin areas.
