Our ability to form and recollect memories is central to our daily life. By associating events across spaces and time, we can retrieve detailed information pertaining to specific experiences in a timely manner. Many previous studies with animals and humans suggested that the hippocampus has a crucial role in this process. However, little is known about the detailed circuits and molecular mechanisms by which the hippocampus processes different phases of episodic memory. By using genetically engineered mice with great spatial and temporal specificity, I uncovered a unique role of the direct entorhinal cortex inputs to the hippocampus in episodic memory formation and the role of calcineurin, a major phosphatase in the brain, in episodic memory retrieval. This improved understanding of how the hippocampus organizes events in temporal context may inform efforts to ameliorate diagnostic tests and treatments for neurological and psychiatric disorders of memory loss.