It has been hypothesised that speed information, encoded by 'speed cells', is important for updating spatial representation in the hippocampus and entorhinal cortex to reflect ongoing self-movement during locomotion. However, systematic characterisation of speed representation is still lacking. In this study, we compared the speed representation of distinct cell types across sub-regions/layers in the dorsal hippocampus and medial entorhinal cortex of rats during exploration. Our results indicate that the preferred theta phases of individual neurons are correlated with positive/negative speed modulation and a temporal shift of speed representation in a sub-region/layer and cell type-dependent manner. Most speed cells located in entorhinal cortex layer 2 represented speed prospectively, whereas those in the CA1 and entorhinal cortex layers 3 and 5 represented speed retrospectively. In entorhinal cortex layer 2, putative CA1-projecting pyramidal cells, but not putative dentate gyrus/CA3-projecting stellate cells, represented speed prospectively. Among the hippocampal interneurons, approximately one-third of putative dendrite-targeting (somatostatin-expressing) interneurons, but only a negligible fraction of putative soma-targeting (parvalbumin-expressing) interneurons, showed negative speed modulation. Putative parvalbumin-expressing CA1 interneurons and somatostatin-expressing CA3 interneurons represented speed more retrospectively than parvalbumin-expressing CA3 interneurons. These findings indicate that speed representation in the hippocampal-entorhinal circuit is cell-type, pathway, and theta-phase dependent. Spatial navigation in humans and animals is an important attribute that enables them to reach their destinations. As part of this process, different brain regions play unique roles in positioning the self in the environment. In particular, 'place cells' in the hippocampus 1 and 'grid cells' in the medial entorhinal cortex (MEC) 2 represent functionally specialised cells that reflect the current location of the animal. To reflect the ongoing self-motion, place cells and grid cells update the associated spatial representation presumably, at least in part, by accessing information regarding the direction and speed of the animal's current movement. 'Head-direction cells' are distributed across multiple brain regions (including the dorsal presubiculum, anterodorsal thalamic nucleus, lateral mammillary nucleus, retrosplenial cortex, entorhinal cortex, and parasubiculum) and encode the direction of the head 3-5 , which is typically the same as the overall direction of ambulation of the animal. Consistent with the concept that head directional information is necessary for generation of grid cell signals 6-8 , disruption of the cell network providing head directional information in the anterior thalamic nuclei would significantly impair both functioning of the grid cells and representation of head direction in the entorhinal cortex and parasubiculum 9. In contrast, it has been suggested that speed is encoded by cont...