Custodian
A custodian in eDiscovery is an individual who has possession, custody or control of potentially relevant electronically stored information, most often an employee whose mailbox, files, chat history and devices are preserved and collected. Custodians are the primary unit of scoping in discovery: the parties negotiate how many, which ones, and over what date range.
Also called: data custodian · records custodian · ESI custodian · custodian list
Updated September 6, 2026
What does a custodian do in eDiscovery?
Discovery is organized around people because that is how data is organized. Each custodian has a mailbox, a home directory, a cloud drive, a set of chat channels and one or more devices. A litigation hold is issued to custodians; collection is executed per custodian; volume, cost and review effort are all estimated per custodian; and the ESI protocol fixes how many custodians each side must search.
The custodian field follows a document through the whole process. It is carried in the load file as CUSTODIAN, and where global deduplication removes copies held by several people, the ALLCUSTODIANS field records everyone who had one, so a document produced once can still be shown to have sat in the CEO’s mailbox.
What does a custodian list look like in practice?
An initial custodian list as it might be exchanged under a protocol:
| Custodian | Role | Date range | Sources |
|---|---|---|---|
| J. Mendez | Operations manager | 2023-01-01 – present | Exchange, OneDrive, Teams, mobile |
| R. Apex | CEO | 2023-01-01 – present | Exchange, OneDrive |
| Payroll (shared) | Non-custodial | 2023-06-01 – present | Shared mailbox |
How does a custodian show up on an eDiscovery invoice?
Per-custodian pricing is common at the front of the process: collection is frequently quoted per custodian or per source, and some providers charge preservation per custodian per month for holds maintained in place. Every custodian added multiplies the processed volume and therefore the per-gigabyte processing and hosting fees. A protocol that allows global deduplication means the tenth custodian’s copy of an email already produced adds review effort only if it is unique. The cost calculator models the multi-matter, multi-custodian effect.
Custodian count drives collection scope, and collection scope drives every volume-based fee that follows. See the cost guide and the per-GB breakdown.
Sources
- Fed. R. Civ. P. 26(b)(1) (proportionality) and 34(a) (possession, custody or control).
- The Sedona Conference Glossary, “custodian.”
Related terms
Litigation hold · Collection · Electronically stored information (ESI) · Deduplication · ESI protocol
eDiscovery at one flat monthly rate
$3,250 a month on a 12-month agreement. No per-user fees and no per-GB hosting charges.
Common questions
What is a custodian interview?
A structured conversation with each custodian, usually by counsel or a discovery specialist, to identify where they keep relevant information (which systems, folders, devices and accounts) and any practices such as personal email or messaging apps that the collection plan must cover. Interviews are documented because they evidence the reasonableness of the search.
How many custodians is reasonable?
There is no fixed number; proportionality under Rule 26(b)(1) governs. Parties commonly agree an initial set of priority custodians and a process for adding more on a showing of relevance. Many ESI protocols set a presumptive cap per side, adjustable by agreement.
What is a non-custodial data source?
A source not tied to one person: a shared mailbox, a departmental file share, a database, a document management system. Non-custodial sources are scoped separately and are frequently the largest in volume.