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This article describes the format and functionality of the Grand Alliance transport bitstream that is intended for the terrestrial broadcast of digital HDTV in the United States. The article begins with an introduction of the HDTV system selection process within the United States, and proceeds with an overview of the Grand Alliance and a description of the Grand Alliance system architecture. The transport functionality and format is then described in detail. The format is based on the use of a fixed-length packet structure, with packet headers to support different communications protocol functions. The advantages of the packetization approach are first described. The format choice is shown to take into account several diverse system requirements including flexibility, robustness, scalability, and simple interoperability of the bitstream with other transmission media such as ATM networks. Higher-layer protocol functionality in the format, including the ability to extract programs, and the elements of these programs, including the video, audio, and data components, from a multiplexed bitstream, are described. The details of the packet format and the functionality of the different header fields are presented.