Kroy IP Holdings, LLC sued Groupon, Inc. for patent infringement. Groupon moved to dismiss, arguing collateral estoppel based on prior Patent Trial and Appeal Board (PTAB) decisions finding other claims of the same patent unpatentable. The district court granted the motion, but the Federal Circuit reversed. The court found that the different burdens of proof between PTAB proceedings (preponderance of the evidence) and district court (clear and convincing evidence) prevented collateral estoppel from applying. Therefore, the case was remanded for further proceedings.