There are necessary participants at every deposition—the deponent, court reporter, counsel—but who else might you encounter? The answer may come as a surprise; in the absence of a protective order, there are no limitations on who can attend.
Federal Rule of Civil Procedure 26(c)(1)(E) places the burden on the party seeking to exclude people from the deposition to move for a protective order “designating the persons who may be present while the discovery is conducted.” To meet this burden, the moving party must show “good cause” that an order is necessary “to protect a party or person from annoyance, embarrassment, oppression, or undue burden or expense.”
Showing good cause requires the party seeking to exclude people from the deposition to make a substantiated and particularized demonstration of “serious harm” if the person to be excluded is allowed to attend.  Conclusory statements of threatened harm are insufficient.
“Serious harm” is a high standard. For instance, unsupported allegations that fact witnesses should be excluded from the depositions of other fact witnesses because, as employees of one of the parties, they “might feel a sense of camaraderie or feel pressure… that might taint their testimony”, is insufficient to warrant a protective order. Thus, in most cases—and unless the court rules otherwise—a party is free to have other attendees at a deposition.
It is not uncommon to invite experts or other witnesses to attend a deposition, as they can play an important role in assisting counsel. Even so, it’s best to provide advance notice to opposing counsel. That way, there will be time to resolve objections in advance, either by agreement or on a motion for protective order. Even if allowed, surprising counsel with an unexpected attendee could, as a practical matter, result in a delay of the deposition until the dispute is resolved.
–Sarah Gohmann Bigelow