A Practice Note discussing the infringement contentions and invalidity contentions that parties litigating a patent case in the US District Court for the District of Delaware typically must exchange early in the case under case-specific scheduling orders and the court's Default Standard for Discovery. This Note discusses the content requirements for infringement and invalidity contentions, best practices for meeting the content requirements, the duty to supplement contentions, motions to amend a party's infringement or invalidity contentions, and motions to strike or compel an adversary to supplement untimely or inadequate infringement or invalidity contentions.