Astrocytic contributions to Alzheimer’s disease (AD) progression were, until recently, largely overlooked. Astrocytes are integral to normal brain function and astrocyte reactivity is an early feature of AD, potentially providing a promising target for preclinical diagnosis and treatment. Several in vivo AD biomarkers already exist, but presently there is a paucity of specific and sensitive in vivo astrocyte biomarkers that can accurately measure preclinical AD. Measuring monoamine oxidase-B with neuroimaging and glial fibrillary acidic protein from bodily fluids are biomarkers that are currently available. Developing novel, more specific, and sensitive astrocyte biomarkers will make it possible to pharmaceutically target chemical pathways that preserve beneficial astrocytic functions in response to AD pathology. This review discusses astrocyte biomarkers in the context of AD. The neurocentric view of AD is evolving and the contributions astrocytes make to the disease’s pathological processes are finally considered. AD pathology triggers astrocyte reactivity, which imaging and fluid biomarkers can measure in vivo. Astrocyte dysfunction in AD could contribute to 18FFDG-PET hypometabolism. Astrocytes are promising targets for developing novel, specific fluid or imaging biomarkers for detecting preclinical AD. Pharmacologically targeting astrocytes may lead to developing an effective treatment for AD.