Synchronization in neuronal systems is a new and intriguing application of dynamical systems theory. Why are neuronal systems different as a subject for synchronization? ͑1͒ Neurons in themselves are multidimensional nonlinear systems that are able to exhibit a wide variety of different activity patterns. Their "dynamical repertoire" includes regular or chaotic spiking, regular or chaotic bursting, multistability, and complex transient regimes. ͑2͒ Usually, neuronal oscillations are the result of the cooperative activity of many synaptically connected neurons ͑a neuronal circuit͒. Thus, it is necessary to consider synchronization between different neuronal circuits as well. ͑3͒ The synapses that implement the coupling between neurons are also dynamical elements and their intrinsic dynamics influences the process of synchronization or entrainment significantly. In this review we will focus on four new problems: ͑i͒ the synchronization in minimal neuronal networks with plastic synapses ͑synchronization with activity dependent coupling͒, ͑ii͒ synchronization of bursts that are generated by a group of nonsymmetrically coupled inhibitory neurons ͑heteroclinic synchronization͒, ͑iii͒ the coordination of activities of two coupled neuronal networks ͑partial synchronization of small composite structures͒, and ͑iv͒ coarse grained synchronization in larger systems ͑synchronization on a mesoscopic scale͒. © 2008 American Institute of Physics. ͓DOI: 10.1063/1.2949925͔The observation of synchrony (coherence, correlation) in the brain and the entire nervous system has a long history. Neuronal synchronization has been experimentally analyzed on many different levels of system complexity. Even though the functional role of this phenomenon is still not absolutely clear, neuroscientists agree that the level of synchrony is one of the key characteristics of the activity of the brain/neuronal systems in general. Both limit cases, too strong and too weak synchronization are characteristic for certain brain disorders, such as epilepsy, Parkinson's disease, Alzheimer's disease, and schizophrenia (see Refs. 1 and 2). In this short review we discuss a few mechanisms of neuronal synchronization that illustrate the specificity of the corresponding phenomena in neuronal circuits, and their similarity to classical examples in physical systems. We also discuss briefly the influence of the complexity of real neuronal systems on synchronous dynamics.