Abstract: Life on Earth has its own rhythm; a 24-hour cycle that guides biological processes from gene expression to behavior patterns. The immune system is modulated by these circadian rhythms, resulting in time-of-day variation in inflammatory responses. Inflammation in the body is sensed by the brain and elicits behavioral changes such as social withdrawal and impaired memory. As we age, both circadian rhythms and immune responses are compromised, and chronic inflammation occurs. My work focuses on the links between these two critical biological systems to investigate how circadian disruption may potentiate neuroinflammation and elicit behavioral changes. Using rodent models, I have identified a key role for the microglial clock in regulating neuroinflammatory responses and behavior, and I have found that manipulation of circadian rhythms in aged mice dampens neuroinflammation and increases sociability. Thus, targeting the circadian system is an exciting new way to tackle age-related neuroinflammation and behavioral changes. Future work will focus on determining the role of circadian rhythms in neuroimmune niches (e.g., the choroid plexus) in regulating brain immunosurveillance and age-related neuroinflammation, and how immune signaling feeds back to the circadian clock to propagate disrupted function. With this work, I aim to identify novel therapeutic strategies to slow cognitive decline and promote healthy aging.