Where are the dinim of multiple wives located?

Question

I know the history, the gezerim, etc., but what I can't find is the practical halachot once one has multiple wives. Where can I find this?

Answer 1

Rambam, Mishneh Torah, Hilchot Ishut 14:3-4;

נוֹשֵׂא אָדָם כַּמָּה נָשִׁים אֲפִלּוּ מֵאָה בֵּין בְּבַת אַחַת בֵּין בָּזוֹ אַחַר זוֹ וְאֵין אִשְׁתּוֹ יְכוֹלָה לְעַכֵּב. וְהוּא שֶׁיִּהְיֶה יָכוֹל לִתֵּן שְׁאֵר כְּסוּת וְעוֹנָה כָּרָאוּי לְכָל אַחַת וְאַחַת. וְאֵינוֹ יָכוֹל לָכוֹף אוֹתָן לִשְׁכֹּן בְּחָצֵר אַחַת. אֶלָּא כָּל אַחַת וְאַחַת לְעַצְמָהּ:‏

וְכַמָּה הִיא עוֹנָתָן. לְפִי מִנְיָן. כֵּיצַד. פּוֹעֵל שֶׁהָיוּ לוֹ שְׁתֵּי נָשִׁים יֵשׁ לָזוֹ עוֹנָה אַחַת בְּשַׁבָּת וְיֵשׁ לָזוֹ עוֹנָה אַחַת בְּשַׁבָּת. הָיוּ לוֹ אַרְבַּע נָשִׁים נִמְצָא עוֹנַת כָּל אַחַת מֵהֶן פַּעַם אַחַת בִּשְׁתֵּי שַׁבָּתוֹת. וְכֵן אִם הָיָה מַלָּח וְיֵשׁ לוֹ אַרְבַּע נָשִׁים תִּהְיֶה עוֹנַת כָּל אַחַת מֵהֶן פַּעַם אַחַת בִּשְׁתֵּי שָׁנִים. לְפִיכָךְ צִוּוּ חֲכָמִים שֶׁלֹּא יִשָּׂא אָדָם יוֹתֵר עַל אַרְבַּע נָשִׁים אַף עַל פִּי שֶׁיֵּשׁ לוֹ מָמוֹן הַרְבֵּה כְּדֵי שֶׁתַּגִּיעַ לָהֶן עוֹנָה פַּעַם אַחַת בְּחֹדֶשׁ:‏

A man [has the prerogative of] marrying several wives - even 100, whether at one time or one after the other. His wife may not object to this, provided he has the means to provide each [wife] with her subsistence, clothing and conjugal rights as befits her. He may not, however, compel his wives to live in the same courtyard. Instead, each one is entitled to her own household.

What are [his obligations with regard to his wives'] conjugal rights? [They are determined according to] the number [of wives he has.]

What is implied? If a worker has two wives, he is obligated to fulfill his duties towards each one once a week. If he has four wives, he is obligated to fulfill his duties towards each one once every two weeks. Similarly, a seaman who has four wives is obligated to fulfill his duties towards each one once every two years.

Therefore, our Sages commanded that a person should not marry more than four wives, although he has ample financial resources, so that he will be able to fulfill his conjugal obligations towards each one once a month.

(Translation courtesy of chabad.org)

This topic is discussed more fully in Shulchan Aruch, Even HaEzer 1:9-12 as well as 76:7-8.

Also relevant is 2:11 which forbids keeping multiple wives in different cities.

Finally, see Rambam, Mishneh Torah, Hilchot Ishut 17:1-3,8,12 regarding rules of priority when paying ketubot to multiple wives.