The dopamine system is involved in motivation, reward and learning, and dysfunction in this system has been implicated in several disorders, including Parkinson's disease (PD) and schizophrenia. Key progress in our understanding of its functions has come from extracellular in vivo electrophysiological recordings from midbrain dopamine neurons. Numerous studies have used a defined set of criteria to identify dopamine neurons electrophysiologically. However, a few recent studies have suggested that a minority population of non-dopamine neurons may not be readily distinguishable from dopamine neurons, raising questions as to the reliability of past findings. We provide an overview of the key findings related to this controversy and assess the criteria used for the electrophysiological identification of dopamine neurons in the substantia nigra pars compacta (SNC) and ventral tegmental area (VTA).