Is it permissible to sit next to a person who is davening Shemoneh Esrei?

It is forbidden to sit within four amos of a person who is davening Shemoneh Esrei. Sitting while another person is davening gives the impression that one is uninterested in being mekabel ol malchus shamayim. If, however, the person who wishes to sit is also davening, he may sit next to the person who is davening Shemoneh Esrei. By davening, he is also participating in kabalas ol malchus shamayim. The poskim disagree about whether learning Torah counts as kabalas ol malchus shamayim. One should be stringent unless he is sitting behind the person who is davening. If the person davening is behind a stand which is ten tefachim high and four tefachim wide, one may sit on the other side of the stand even if he is within four amos of the person davening.

סי' ק"ב ס"ק ב' ג' ו' ז' ביאורים ומוספים דרשו 7

Is it permissible to sit and daven in front of a person who is davening Shemoneh Esrei?

It is also forbidden to sit in the vicinity of a child who is the age of chinuch and is davening. Some Rishonim hold that it is forbidden to sit in the line of sight of a person who is davening, even if one is davening himself and is not within the davener’s four amos. It gives the impression that the person who is davening is bowing to the person sitting in front of him. Practically, one only has to be stringent about sitting four amos (or less) in front of someone who is davening. A weak person who does not have a place to sit outside the four amos of someone who is davening may sit within his four amos. He should not sit in front of him, however. 

ס"א וס"ב ס"ק ח-י ביאורים ומוספים דרשו 4

May one walk in front of a person who is davening Shemoneh Esrei?

There is a separate halacha that one may not walk in front of a person who is davening Shemoneh Esrei. Walking in front of him may disturb him. In addition, walking in front of someone who is davening creates a separation between that person and the Shechinah. The Achronim disagree about whether one may walk within the peripheral vision of someone who is davening. Shulchan Aruch permits walking by the side of a person who is davening (i.e. outside of his visual field). The Zohar, however, does not allow walking beside a person who is davening. For the sake of certain mitzvos, walking in front of a person who is davening is permitted (e.g. to complete a minyan or to go up to duchen). The poskim disagree about whether it is permissible to walk in front of a person who is davening in order to wash hands for duchening.

ס"ד ס"ק ט"ו- י"ז ביאורים ומוספים דרשו 21 22

• If someone in shul is davening out loud and one hears him completing a brocha, the poskim disagree about whether to answer Amen. Some say not to respond, since the person who said the brocha out loud is davening in an improper way.

• Lashon Hakodesh is the preferred language for davening. Lashon Hakodesh contains many segulos, and it was used by the Ribono Shel Olam when he spoke with his nevi’im. In addition, it was the language used by the Anshei Knesses Hagedolah when they instituted davening.

• One of the practices of the maskilim was to change the text of the davening from Lashon Kodesh to the local language. Their intentions were to cause Jews to forget their connection to Lashon Kodesh, which would in turn cause them to lose their connection to Eretz Yisroel and their yearning for Moshiach. They also began to omit the brochos of kibbutz galuyos and binyan Yerushalayim. The Achronim who lived at the time fought valiantly against their reforms and changes to the mesorah.

• Can one take three steps back if the person behind him is davening Shemoneh Esrei?

• What is the proper way to deal with a disturbing child in the middle of Shemoneh Esrei?

• What should a Rov do if he does not want the tzibur to wait for him to begin Shemoneh Esrei?