The second, third and fourth Shabbosos we read Parshiyos Zachor, Parah Adumah and ha'Chodesh. The fifth Shabbos we resume the normal order.

We interrupt (the normal order) for all of the following - Rosh Chodesh, Chanukah, Purim, Ta'aneisim, Ma'amados, and Yom Kipur.

(Gemara - R. Ba citing R. Chiyah bar Ashi): We do not interrupt between Purim and [Parshas] Parah.

(R. Levi citing R. Chama bar Chaninah): We do not interrupt between Parah and [Parshas] ha'Chodesh.

(R. Levi): A Siman for when we read these Parshiyos - "[at the Seder] between these cups (the first two, or the second and third), if he wants to drink, he may drink. Between the third and fourth cups, he may not drink." (Likewise, we can interrupt between the first two Parshiyos, or between the second and third, but not between the third and fourth.)

(R. Levi citing R. Chama bar Chaninah): It would be proper for ha'Chodesh to precede Parah, for the Mishkan was erected on the first of Nisan, and the Parah was burned on the second [of Nisan]!

So why is Parah earlier? It is the Taharah of all Yisrael.

Question (Yirmeyah the scribe, to R. Yirmeyah): If Rosh Chodesh fell on Shabbos, what do we read? [The Mishnah said that we interrupt for Rosh Chodesh. Does this refer to Kri'as ha'Torah, or the Haftorah?]

Answer (R. Yirmeyah): We read [all seven Aliyos in Parshas Musaf of] Rosh Chodesh.

Support (R. Chelbo, in front of R. Eimi): Our Mishnah teaches so! We interrupt for everything - Rosh Chodesh, Chanukah, Purim, Ta'aneisim, and Ma'amados. (There is no Haftorah on Ta'aneisim and Ma'amados. The Mishnah must discuss Kri'as ha'Torah!)

Question (Yitzchak Sechorah to R. Yitzchak): If Rosh Chodesh falls on Chanukah, what do we read?

Answer (R. Yitzchak): Three read in Rosh Chodesh, and one reads in [Korbanos ha'Nesi'im, which we read on] Chanukah.

(R. Pinchas citing R. Simon citing R. Aba bar Zemina, and some say in the name of Rav Avodimi of Chaifa): Three read in Chanukah, and one reads in Rosh Chodesh. This teaches you that the fourth comes only for Rosh Chodesh. (On Chanukah, only three read.)

Question (Bar Shilmiya the teacher, to R. Mana): Exert yourself [to answer this]! If Rosh Chodesh of Chanukah fell on Shabbos, do not seven read [on Shabbos in any case]? Can you say that the fourth comes only for Rosh Chodesh?!

R. Mana: Is this a teacher's question?! (This is a child's question! There is no obligation to publicize that four read on Rosh Chodesh, just when it is possible, we do so!)