Who is the third umpire, and when is DRS used in a Test?

DRS requires, as a minimum, the mandatory camera set-up plus approved ball-tracking technology and approved sound-based edge detection technology.

• With DRS: the ICC appoints the third umpire, who must not be from the country of either team, and who handles both Umpire Reviews and Player Reviews. The ICC also appoints an independent technology expert (the ICC Technical Officer) to attend every series where DRS is used, to assist the third umpire and protect the integrity of the process.
• Without DRS: the Home Board appoints a third umpire from its own country, who handles Umpire Reviews only and may use only replays of camera images (no ball-tracking or edge detection).

Source: ICC Men's Test Match Playing Conditions (effective from October 2026), Appendix D, paragraph 1.1.