A nexus is a connection linking two or more things.

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In the context of VA Medical Center (VAMC) Compensation and Pension (C&P) claims, a nexus letter is a document written by a medical provider that clearly explains how an in-service event caused the claimant’s current medical condition. This letter can be included in your claims file as evidence and can significantly improve your chances of being granted service connection or receiving an increase for an already service-connected condition.