Posture During the Eucharistic Prayer

Should people stand or kneel during the eucharistic prayer?

This is answered in the General Instruction of the Roman Missal, number 43:

...In the Diocese of the United States of America, they should kneel beginning after the singing or recitation of the Sanctus until after the Amen of the Eucharistic Prayer, except when prevented on occasion by reasons of health, lack of space, the large number of people present or some other good reason. Those who do not kneel ought to make a profound bow when the priest genuflects after the consecration. The faithful kneel after the Agnus Dei unless the diocesan Bishop determines otherwise.