Having the administrative and clinical information concerning the patient presented in a comprehensible format, language, and terminology is valuable for any healthcare provider. In Europe, this type of information is represented by the Patient Summary Guideline and on the other side of the Atlantic by the Continuity of Care Document (CCD). Trillium Bridge is a project co-funded by the European Commission that “compares specifications of EU and US patient summaries with the aim of developing and testing common and consistent specifications and systems enabling interoperability of electronic health records across the Atlantic.” The objective of this article is to summarize the findings of the comparison between these two Patient Summaries. Both documents are using the same syntax, namely Clinical Document Architecture (CDA), making the comparison easier. The documents were compared from a clinical, syntactic, and terminological point of view focusing on semantic interoperability. A common denominator was found in terms of sections, data elements, and value sets. Comparing the value sets led the project team to assess available official maps such as the SNOMED CT and ICD-10 and determine their applicability. In some cases, such as the National Cancer Institute Thesaurus and the EDQM standard terms, no maps were found and the team proposed associations. The common denominator thus identified allows for significant parts of the data to be exchanged, setting the baseline for the transatlantic exchange of a meaningful set of patient summary data and establishing a springboard for an international patient summary standard.