The thalamus is a nuclear complex situated in the diencephalon. Besides a neuro-anatomical description of the thalamus, this article reviews the current knowledge on the functional anatomy of the three functional classes of thalamic nuclei: specific, non-specific and association nuclei. As the majority of the pathology affecting the thalamus is of cerebrovascular origin, the vascularisation of the human thalamus will be reviewed as well. Finally, the knowledge of the functional anatomy and the vascularisation of the human thalamus will be integrated in the review of the semeiology of thalamic syndromes. Besides its function as a relay centre in subserving sensory and motor mechanisms, the thalamus participates in various neurocognitive processes such as memory and language. The current knowledge on these topics will be reviewed as well.