Introduction Metadata is an exceedingly broad category of information covering everything from an object's title and date of origin to information about layout, presentation, and rights. Within libraries and digital object repositories, metadata is the cornerstone of the infrastructure required for exchange and use of information. While metadata standards abound, and acceptance and use of these standards is equally widespread, agreement on a common standard is much harder to find. This dilemma was highlighted for the Los Alamos National Laboratory Research Library's Library Without Walls Team in the fall of 2003. At that time, it was decided to implement a standards-based digital object repository to hold the library's 80 million metadata records, 1.5 million full-text records, and several million other complex digital objects. A Repository Team was formed to tackle the project. It was recognized that there was a need to convert the disparate metadata to a consistent vendor-neutral format in order to simplify the increasingly complex task of storing, indexing, exchanging, and displaying the records. The process of determining a suitable standard involved definition of requirements, comparison of available standards, formalization of the adopted standard, and, finally, evaluation of the efficacy of the selected standard.