The procession through the nave and up to the foot of the altar by the altar party at the beginning of mass.

Usually during the Entrance Hymn, starting with the first sung verse.

There is no Entrance Procession or Entrance Hymn at low masses.

At the solemn mass, the entrance procession is led by the thurifer with the boat boy at his side.

At a sung mass, the entrance procession is led by the crucifer with the candle bearers at his side.