2012 World Junior Championships in Athletics – Men's 800 metres

The men's 800 metres at the 2012 World Junior Championships in Athletics was held at the Estadi Olímpic Lluís Companys on 13, 14, and 15 July.

Prior to the competition^[update], the existing world junior and championship records were as follows.

Qualification: The first 3 of each heat (Q) and the 3 fastest times (q) qualified

Qualification: The first 2 of each heat (Q) and the 2 fastest times (q) qualified

According to an unofficial count, 60 athletes from 41 countries participated in the event.