Initiative determines the order of turns during combat. When combat starts, every participant rolls Initiative; they make a Dexterity check that determines their place in the Initiative order. The GM rolls for monsters. For a group of identical creatures, the GM makes a single roll, so each member of the group has the same Initiative. See also “Surprise”.
Initiative Order. A combatant’s check total is called their Initiative count, or Initiative for short. The GM ranks the combatants, from highest to lowest Initiative. This is the order in which they act during each round. The Initiative order remains the same from round to round.
Ties. If a tie occurs, the GM decides the order among tied monsters, and the players decide the order among tied characters. The GM decides the order if the tie is between a monster and a player character
Initiative Scores. Sometimes a DM might have combatants use their Initiative scores instead of rolling Initiative. Your Initiative score equals 10 plus your Dexterity modifier. If you have Advantage on Initiative rolls, increase your Initiative score by 5. If you have Disadvantage on those rolls, decrease that score by 5.