This tutorial guideline helps the user to understand Abstract Syntax Notation One (ASN.1)@ the international standard language for defining and encoding data elements in the open systems environment. ASN.1 provides for a more precise specification of message fields and other data@ improving interoperability and reducing costs. TG-9 familiarizes the reader with the ASN.1 concepts in ISO/IEC 8824@ Specification of ASN.1 and ISO/IEC 8825@ Specification for Basic Encoding Rules for ASN.1@ without requiring the reader to read the international documents.