Abstract : Metadata--data about data--arise in many contexts, from many diverse sources, and at many levels in ATLAS. Familiar examples include run-level, luminosity-block-level, and event-level metadata, and, related to processing and organization, dataset-level and file-level metadata, but these categories are neither exhaustive nor orthogonal. Some metadata are known a priori, in advance of data taking or simulation; other metadata are known only after processing--and occasionally, quite late (e.g., detector status or quality updates that may appear after Tier 0 reconstruction is complete). Metadata that may seem relevant only internally to the distributed computing infrastructure under ordinary conditions may become relevant to physics analysis under error conditions ("What can I discover about data I failed to process?"). This talk provides an overview of metadata and metadata handling in ATLAS, and describes ongoing work to deliver integrated metadata services in support of physics analysis.