The U.S. Equities ASID Lookup dataset covers all listed and delisted U.S. equity securities, including common stocks, ETFs, ETNs, ADRs, preferred stocks, warrants, and related instruments, from 2007 to the present. The dataset captures ticker symbols and their effective date ranges, enabling accurate tracking of securities across symbol changes over time. This dataset is designed to support continuous pricing and reference history construction in cases where a security’s internal identifier changes. algoseek assigns each security a SecId, which remains stable across name and ticker changes but may change following certain security restructurings (for example, reclassification events). To preserve continuity across such identifier changes, algoseek introduces a higher-level persistent identifier, ASID (algoseek Security ID). An ASID remains constant for the entire economic life of a security and links together all related SecIds associated with that security over time. The ASID Lookup dataset therefore provides the authoritative mapping needed to chain SecIds and maintain uninterrupted historical time series across complex lifecycle events.