A Timeline is an append-only, tamper-evident personal or institutional event log. It records entries associated with one timeline identity, account, actor, service, organization, document, or provider-defined context. It can be used as private storage, shared selectively with other parties, made public, or connected to Blue documents through Timeline Channels. Blue document processing is one use case of timelines, not the definition of a timeline. A Timeline Provider supplies infrastructure for timelines. Its core responsibilities are to authenticate and authorize parties that append entries to a timeline, store entries in append-only order, assign or record ordering timestamps, link entries to previous entries where the timeline design requires a hash chain, expose entries to authorized readers, and issue completeness/finality guarantees. A provider generally does not understand the business meaning of every message. Someone may place arbitrary Blue messages on a timeline if the provider allows that party to append to that timeline. Documents that later consume those entries decide whether the messages are relevant, valid, authorized, or policy-compliant. Completeness is the guarantee that makes deterministic multi-party processing possible. When a provider says there are no entries with timestamp less than T, it is also promising that future entries it accepts will not be assigned a timestamp less than T. A managed provider can preserve this by assigning monotonically advancing timestamps. A blockchain-backed provider can provide the same kind of guarantee only for finalized history and must define the finality rule. Completeness is about ordering and absence of earlier entries; it is not a claim that message content is semantically valid for a particular Blue document. Timeline entries are normally hash-linked through `prevEntry`, making tampering detectable. Timestamps establish ordering; actor and source fields establish attribution; message contains the Blue payload. A Blue processor may use entries from several timelines, but it should do so only after the relevant providers or finalized stores establish a complete processing window. This lets independent processors merge individual perspectives deterministically without global consensus.