Astrocytes represent the most abundant glial type of the central nervous system (CNS). They perform functions in neurotransmission and neuronal nutrition; however, their involvement in CNS homeostasis is pivotal. As protectors and keepers of the brain, astrocytes detect and respond to various signals. In situations with pronounced disruption in homeostasis, such as during brain ischemia, astrocytes suppress glutamate toxicity by up-taking increased amounts of glutamate and potassium ions; nevertheless, this is only possible until they reach their capacity. After this turning point, astrocytic channels and transporters run in reversed mode, releasing harmful substances, and thus worsening the overall impact of ischemia. Besides regulating the concentration of solutes, astrocytes also control water transport via transient receptor potential vanilloid 4 and aquaporin 4 channels. These are the key players in the development of cerebral edema during ischemia, which can be analyzed employing various methods. Our department specializes in the morphological, structural, and functional studies of astrocytes in acute tissue sections, which will also be discussed in this chapter. Taken together, the role of astrocytes in the pathophysiology of brain ischemia is indisputable, while detailed elucidation of their functions in brain slices may help introduce novel therapeutic approaches to the treatment of stroke.