Gemara

(Rav Huna bar Yehudah): One should finish reading the weekly Torah portion, twice in Mikra (Lashon ha'Kodesh) and once in the Targum (Onkelus' Arame'ic translation), with the Tzibur.

This applies even to a verse such as "Ataros v'Divon."

One who finishes the Parshiyos with the Tzibur is rewarded with lengthened days and years.

(Beraisa): One may not read the Parshiyos before or after (the Tzibur).

R. Yehoshua ben Levi (to his sons): Finish the Parshiyos, twice in Mikra and once in Targum, with the Tzibur.

Megilah 4a (R. Yehoshua ben Levi): One must read the Megilah at night, and Lishnosah by day.

(R. Yirmeyah): This means to repeat (the reading), like one who says 'I will finish this Parshah, and repeat it.'

Rishonim

Rambam (Hilchos Tefilah 13:25): Even though one hears the entire Torah every year b'Tzibur, he must read for himself the Parshah of that week. He reads the Parshah twice, and the Targum once. For a verse without Targum, he reads the verse three times. He must finish the Parshiyos with the Tzibur.

Rosh (1:8): One must say Shnayim Mikra v'Echad Targum even for a verse such as "Ataros v'Divon." Rashi explains that it has no Targum. This is difficult. If so, it could have said "Reuven v'Shimon (Levi vi'Yehudah)" (Shemos 1:2) or similar verses! Rather, it mentioned this verse for in some Seforim it is translated, and also in the Yerushalmi it is translated. One explanation says that we chose this verse, even though there is not such a need to translate it. (It lists cities taken from Sichon and Og.) The Targum Yerushalmi explains the significance of the names.) One need not say three times verses such as "Reuven v'Shimon..." In any case, the custom is to be stringent like Rashi. Some say that Targum into any other language is acceptable for those who speak the language. Targum is for ignoramuses who do not understand Lashon ha'Kodesh. This is wrong. The Targum explains many things that we cannot understand from the Mikra itself. Rav Yosef said 'if not for the Targum of this verse (we would not know...)' It seems that one who reads a Perush of the Torah is Yotzei, for it explains every word.

R. Yonah (4b DH v'Afilu): For a verse such as "Ataros v'Divon," which has no Targum Onkelus, only Targum Yerushalmi, one must say the Yerushalmi. For a verse without any Targum, it suffices to say the verse twice. Perhaps one must say it three times.

Rosh: The entire week is called with the Tzibur, since we start reading from Minchah of the previous Shabbos, even though only from Wednesday and onwards is called 'before Shabbos.' Rebbi commanded his sons not to eat bread (on Shabbos morning) until finishing the Parshah. However, if he did not finish before eating, he finishes after eating.

Poskim

Shulchan Aruch (OC 285:1): Even though one hears the entire Torah every year b'Tzibur, he must read for himself the Parshah of that week. He reads the Mikra twice and the Targum once, even for a verse such as "Ataros v'Divon."

Taz (1): According to Rashi, we can say that the Gemara did not mention "Reuven v'Shimon..." because they are names of the Shevatim, and surely they have great Kedushah. Ataros v'Divon are names of cities of Eretz Yisrael. Perhaps the Nochrim picked these names! Even so, one must read them three times.

Magen Avraham (1): The Shlah and Maharshal say that one reads every Parshah twice, and then the Targum. Megilah 4a connotes like this. However, Divrei Chamudos (Berachos 1:41) rules that one reads every verse twice, and then the Targum, and so say Hagahos Yesh Nochlin in the name of the Ari Zal and Seder ha'Yom, and Kesavim. Siman 145:1 connotes that this was the custom when they used to translate the Torah (after reading it b'Tzibur). They would say the last verse after the Targum, in order to end with Torah. If he is fluent in the Ta'amim (notes for reading the Torah), he should read in a Sefer Torah and immerse after reading. I will not deal with hidden matters (of Kabalah). He should cut his fingernails before reading.

Gra: This is unlike Ra'avan, who says that only an individual who did not hear Keri'as ha'Torah (must read Shnayim Mikra v'Echad Targum). Presumably, Rav Bivi was not alone, and all the more so according to R. Chananel's text, that he was at Kalah where there were many people (and even so, he read Shnayim Mikra v'Echad Targum).

Mishnah Berurah (2): One should not read once Mikra and once Targum and intend to hear (Mikra a second time) from the Ba'al Korei. Rather, he must read Shnayim Mikra apart from what he hears from the Ba'al Korei, unless he read it with his mouth along with the Ba'al Korei. B'Di'eved, one was Yotzei through what he heard from the Ba'al Korei (Magen Avraham 8). Some are stringent even b'Di'eved. Some say that one should read every verse twice and then its Targum. Some say that he reads every Parshah twice, and then its Targum. I.e. he reads every open or closed Parshah (these are marked off with a Pei and Samech in our Chumashim) twice, and then the Targum. The Magen Avraham and Sha'arei Teshuvah favor the first opinion. The Gra read the Targum after (finishing) every open or closed Parshah, or after a place that appears like a bigger break of the matter. However one did is fine.

Mishnah Berurah (6): It is good if one does not interrupt Shnayim Mikra v'Echad Targum for anything. Meticulous people do so, and every Ba'al Nefesh should do so.

Kaf ha'Chayim (15): Mekubalim say to read the entire Parshah at once. If he is very thirsty, he may drink water in the middle.

She'elas Rav (ha'Gaon R. C. Kanievsky Shlita, 2:25:12,14,15): Shnayim Mikra v'Echad Targum is like any Divrei Torah regarding interrupting. One interrupts for a great need, e.g. if he must honor someone.

Kaf ha'Chayim (3): On Erev Shabbos, after Shacharis, the Ari Zal would fulfill Shnayim Mikra v'Echad Targum. He read each verse twice from a Sefer Torah, and a Talmid read the Targum from a Sefer, and the Ari Zal repeated it. If he could not do so on Erev Shabbos due to Ones, he did so on Shabbos, after Shacharis before eating.

Kaf ha'Chayim (4): The Magid rebuked the Beis Yosef for reading Shnayim Mikra v'Echad Targum quickly, like a burden he seeks to relieve himself of. One should read it slowly, to perceive the difficulties and answer them. What one cannot answer, he should look at Meforshim.

Kaf ha'Chayim (5): One must read each verse all at once. In the 10 utterances, "Lo Sirtzach Lo Sinaf... Ed Shaker" is one verse.

Kaf ha'Chayim (6): One says the Targum at the end, not in the middle. Shnayim Mikra v'Echad Targum connotes like this, and so say some Meforshim, the Zohar and the Mekubalim.

Kaf ha'Chayim (8,9): The Radvaz and Machazik Berachah say that if one heard Shnayim Mikra v'Echad Targum word for word, he was Yotzei, even if there was no Ones. However, it is better to say it oneself. If one was sick, he is exempt, and he need not hear it from others. However, he should say it after he recovers, so his Mitzvah will not be deficient that year.

Kaf ha'Chayim (14): The Ari Zal says not to say Shnayim Mikra v'Echad Targum at night, for one should not say Targum at night.

Ashrei ha'Ish (2:11:7, citing ha'Gaon R. Y.S. Elyashiv Ztz"l Shlita): One may say Shnayim Mikra v'Echad Targum at night.

She'elas Rav (2:25:16): It is better to say Shnayim Mikra v'Echad Targum during the day.

Note: Even the stringent opinion does not forbid Mikra at night, just it is better to learn it during the day - Sha'ar ha'Tziyun 238:1.

Shulchan Aruch (2): If he learned the Parshah with Rashi's Perush, this is considered like Targum. One who fears Shamayim will read the Targum and also Perush Rashi.

Beis Yosef (DH v'Im): Semag says that the Perush helps more than Targum. The Mordechai and Hagahos Maimoniyos bring this. However, Semag and Hagahos Maimoniyos bring that the Ri, Rav Amram Gaon and R. Natrunai Ga'on disagreed. The Targum merited (that we say it with the Mikra) because it was given on Sinai. One who fears Shamayim will fulfill all opinions, and read the Targum and Perush Rashi.

Taz (2): One with Yir'as Shamayim should read the Parshah itself in a Sefer Torah at least once, and a second time with the Ba'al Korei. One is not properly Yotzei through reading in a Chumash, for we require 'Devarim (Torah) shebi'Chsav', i.e. from a complete, proper Sefer Torah. One can complete this until Simchas Torah. This is my custom. The Tur says that one is not Yotzei through other translations, i.e. one who could understand Perush Rashi. If one cannot understand Perush Rashi, surely it is proper to read a Perush of the Torah in Lashon Ashkenaz nowadays, such Tze'enah u'Re'enah or similar Perushim, in order to understand the Parshah.

Mishnah Berurah (5): The Perush must be based on Perush Rashi and other Chachamim, based on the Gemara.

Magen Avraham (3): Perush Rashi is primary, for it is based on the Gemara.

Magen Avraham (4): If one does not have Targum, he reads Mikra twice, and when he gets Targum, he reads it.

Mishnah Berurah (4): If one read a translation in another language that explains only the words, he was not Yotzei, for the Targum explains more than just the words.

Mishnah Berurah (5): One is Yotzei through reading Mikra twice and Perush Rashi once. If a verse has no Perush Rashi, he reads it three times.

Mishnah Berurah (6): It is proper for everyone to learn every week the Parshah with Perush Rashi in addition to Targum, for many Parshiyos, especially in Vayikra, that cannot be understood through the Targum alone. One must read in order. One may not read the Targum first. Rather, first he reads Shnayim Mikra, and afterwards Targum.

Kaf ha'Chayim (22): The Yam Shel Shlomo (Kidushin 2:14) says that if one does not have time for Targum and Perush Rashi, Perush Rashi is better. The Mekubalim say that the Targum is better.

Kaf ha'Chayim (23): Even if one may not read Targum at night, he may learn Perush Rashi at night.