Enactment of Maariv
1. Yaakov. The Tannaim and Amoraim have a machlokes about the origins of Maariv. Some hold Yaakov instituted it, as it says (פ' ויצא כ''ח, י''א ), “ויפגע במקום וילן שם”; Chazal explain that one meaning of the word “ויפגע” is to daven (ברכות דף כ''ו ע''ב ). We learn from here that Yaakov Avinu instituted the Maariv tefilla (רש''י עה''ת ).
2. Korban tamid. Others hold the tefillos were instituted by Anshei Knesses HaGedola corresponding to the korban tamid (רש''י ברכות שם ): Shacharis parallels the morning tamid; Mincha, the afternoon tamid; and Maariv, the offering of the limbs and fats which were not consumed by evening, which is done all night (גמ' ברכות שם ). Everyone agrees that the times for the tefillos were established according to the times when the korbanos were brought (או''ש פ''ג תפילה ה''ט ).
Optional [רשות ] or Required [חובה ]?
3. There is a machlokes Tannaim whether Maariv is optional or required (ברכות כז :); Abaye and Rava also have a machlokes about this. The halacha follows Rava, who holds Maariv is optional, but the minhag of all Jews everywhere is to daven Maariv, and they accepted it as a chiyuv (רמב''ם פ''א תפלה ה''ו ). Some halachos of Maariv emerge from the fact that it was technically established as optional.
4. Chazaras HaShatz. There is no Chazaras HaShatz at Maariv. Since at its essence it is optional, Chazal did not obligate a shliach tzibbur to be motzi everyone. Our acceptance of it as a chiyuv is not strong enough to burden the tzibbur with Chazaras HaShatz (מ''ב סי' רל''ז סק''א ).
5. Women. The poskim also hold that for this reason, Maariv for women retains its original optional status. They did not accept it upon themselves as a chiyuv to daven Maariv, and most of them do not daven Maariv (מ''ב סי' ק''ו סק''ד ).
6. סמיכת גאולה לתפילה. Although it has been established as a proper chiyuv, it is not a full-fledged chiyuv with respect to saying things necessary for davening between גאל ישראל and Shemoneh Esrei. Thus, one may announce “Yaaleh v’Yavo” or “Al HaNissim” between גאל ישראל and Shemoneh Esrei even though one who forgets them does not repeat Shemoneh Esrei (שעה''צ סי' רל''ו סק''ד).
