Joanna Chen The Federal Circuit has ruled on an important issue surrounding the claim construction of a preamble of a patent claim in Simo Holdings Inc v Hong Kong Ucloudlink Network Technology Ltd (2019-2411 (5 January 2021)). The key takeaway is that, in addition to being limiting when a claim preamble serves as an antecedent basis for a claim term appearing in the body of the claim, a preamble can also be limiting when it supplies “essential structure” and the body of the claim does not define “a structurally complete invention”. The patent at issue, US Patent 9,736,689 (the ’689 patent), owned by SIMO Holdings Inc, describes apparatuses and methods for reducing roaming charges on cellular networks outside a home territory. SIMO sued Hong Kong uCloudlink Network Technology Limited and uCloudlink (America), Ltd (collectively, uCloudlink) for infringement. Four of uCloudlink’s products were alleged to infringe Claim 8 of the ’689 patent, which recites the following preamble followed by a list of functional steps: