Mixed 4 × 400 metres relay

The mixed 4 × 400 metres relay is a mixed-sex 4 × 400 metres relay in which teams field two men and two women. Since March 2022, team members have to run in the order man-woman-man-woman. It was introduced at the 2017 IAAF World Relays and was then held at the 2019 World Athletics Championships in Qatar.

Background
Part of the rationale for the event was that should teams put their men and women in different orders, there will be excitement in seeing large leads being reversed when men and women are running against each other. All the teams in the finals at the 2017 IAAF World Relays ran man-woman-woman-man. In the final of the event's World Athletics Championship debut in 2019, all but one team chose a man-woman-woman-man order, with the exception of Poland, who chose man-man-woman-woman. In March 2022, the rule was changed so that every team must use the order man-woman-man-woman.

Michael Johnson commentating at the 2019 World Athletics Championships expressed a concern that, while entertaining, the mixed 4 × 400 metres event contributes to an overly busy schedule.

Poland won the inaugural Olympic 4 × 400 metres mixed relay at the 2020 Summer Olympics, held in 2021.

World record progression
The first world record recognised by the IAAF was set by the US team at 3:12.42 in the first heat at the 2019 World Athletics Championships on 28 September 2019, beating a prior world best by the US set in 2016. The US team then set a new record of 3:09.34 in the final the next day. During the 2023 World Athletics Championships, team USA bested the previous record with a time of 3:08:80.