This CEN Technical Specification (TS) contains the mapping between the semantic data model of an electronic invoice (EN 16931-1) and the following syntax: UBL 2.1. For each element in the semantic model (including sub-elements or supplementary componentts sucha as Code List identifiers) it is defined which element in the syntax is to be used to contain its information contents. Any mismatches between semantics, format, cardinality or structure are indicated. Any rules to be followed when using the specific syntax are stated informally in this TS. Together with this TS a set of validation artefacts is published, including formalisation of the rules.