The brain controls spatial navigation in mammals by activating functionally specialized cell types in the medial temporal lobe. Key components of the spatial mapping system are place cells and grid cells. It has been known for some time that place cells are located in the hippocampus and are active only when the animal is entering a specific location in the environment. Here, we present our research results relating to grid cells. We found that grid cells are located upstream of the hippocampus, in the medial entorhinal cortex, and are activated whenever an animal enters locations that are distributed in a spatially periodic pattern across the environment. Moreover, we discovered that the grid cell network is intrinsically organized as grid cells clustered in distinct and independent grid maps with distinct scales, orientations and asymmetries, as well as distinct grid patterns of temporal organization.