克雷芒三世（约1029年－1100年9月8日），原名Guibert of Ravenna，被反对教宗额我略七世的神圣罗马帝国皇帝亨利四世立为教宗。罗马天主教会视其为「伪教宗」，在位期间：1080年6月25日—1100年9月8日。

亨利四世和额我略七世因主教叙任权长期争斗。1080年，因额我略七世第二次绝罚亨利四世，亨利四世遂在布雷萨诺(Brixen)召开宗教会议废黜额我略七世，并推选对立教宗克雷芒三世。1084年3月亨利四世占领罗马，额我略七世出逃。3月24日，克雷芒三世在拉特朗大殿正式登位。3月31日，克雷芒三世为亨利四世加冕。不过克雷芒三世和亨利四世很快被额我略七世请来的诺曼人赶出罗马。

Guibert or Wibert of Ravenna (c. 1029 – 8 September 1100) was an Italian prelate, archbishop of Ravenna, who was elected pope in 1080 in opposition to Pope Gregory VII. Gregory was the leader of the movement in the church which opposed the traditional claim of European monarchs to control ecclesiastical appointments, and this was opposed by supporters of monarchical rights led by the Holy Roman Emperor. This led to the conflict known as the Investiture Controversy. Gregory was felt by many to have gone too far when he excommunicated the Holy Roman Emperor Henry IV and supported a rival claimant as emperor, and in 1080 the pro-imperial Synod of Brixen pronounced that Gregory was deposed and replaced as pope by Guibert.