Based on the European style market contextual model (IEC 62325-351), this particular part of IEC 62325 series specifies a UML package for the acknowledgment business process and its associated document contextual model, assembly model and XML schema for use within the European style electricity markets. The relevant aggregate core components (ACCs) defined in IEC 62325-351 have been contextualised into aggregated business information entities (ABIEs) to satisfy the requirements of the European style market acknowledgment business process. The contextualised ABIEs have been assembled into the acknowledgment document contextual model. A related assembly model and an XML schema for the exchange of acknowledgement information between market participants is automatically generated from the assembled document contextual model. This new edition of IEC 62325-451-1 contains a new optional class and associations required to comply with new business development for European style market. In particular, the following changes have been made: " Addition of an optional attribute ProcessType to the acknowledgement document to ease routing of incoming acknowledgement document instances to the appropriate application. " Clarify the activity diagram for the acknowledgement process. " Add the list of constraints on datatypes.