Video Assistant Referees (VAR) technology will be used in the Champions League and Europa League competitions for the first time this week
European football's governing body confirmed the move following the meeting of its executive committee in Dublin in December.
VAR will also be used at next summer's Nations League Finals - which will feature England as well as Portugal, Holland and Switzerland.
Having been trialled at the World Cup in Russia, as well as certain FA Cup and League Cup fixtures in English football, the technology will also be used in the Premier League from next season after clubs agreed the introduction in principle at a meeting in November.
How VAR works
VAR operates on a three-step process of incident, review/advice, decision, and across the four jurisdictions of football deemed 'game changing' by Fifa.
The IFAB says VAR is only to be used "to correct clear errors and for missed serious incidents" in those "match-changing" situations.
VARs and other match officials are able to recommend reviews, but the only person who can initiate one is the referee, who will then have the final say on whether their original decision should stand or be changed.
They have the option to review footage themselves on a pitch-side monitor before making a final decision.
Goals
VARs are used here to help the referee determine whether an infringement was made that should result in the goal not being awarded.
Penalties
Here, VAR will look to ensure that the correct decision was made regarding the award or non-award of a penalty.
Red cards
Much like with penalty decisions, VAR will look to ensure that the correct decision was made.
Mistaken identity
VAR will clarify which players should be cautioned or sent off, or correct the referee in the event of mistaken identity.
