IEC TR 62541-1:2016(E) is a Technical Report and presents the concepts and overview of the OPC Unified Architecture (OPC UA). Reading this document is helpful to understand the remaining parts of this multi-part document set. Each of the other parts is briefly explained along with a suggested reading order. This second edition cancels and replaces the first edition of IEC TR 62541-1, published in 2010. This edition includes no technical changes with respect to the previous edition but includes updates to reflect changes or additions in normative parts of IEC 62541.