Rambam opens the laws of theft by defining theft broadly as taking another's property without permission and discusses the moral and legal status of wrongful taking. This is a key halakhic base for thinking about plagiarism as theft of credit, labor, or intellectual product.
כָּל הַגּוֹנֵב מָמוֹן מִשְּׁוֵה פְּרוּטָה וּלְמַעְלָה עוֹבֵר עַל לֹא תַּעֲשֶׂה שֶׁנֶּאֱמַר (ויקרא יט יא) "לֹא תִגְנֹב". וְאֵין לוֹקִין עַל לָאו זֶה שֶׁהֲרֵי נִתָּן לְתַשְׁלוּמִין שֶׁהַגַּנָּב חִיְּבַתּוּ תּוֹרָה לְשַׁלֵּם. וְאֶחָד הַגּוֹנֵב מָמוֹן יִשְׂרָאֵל אוֹ הַגּוֹנֵב מָמוֹן עַכּוּ"ם וְאֶחָד הַגּוֹנֵב אֶת הַגָּדוֹל אוֹ אֶת הַקָּטָן: אָסוּר לִגְנֹב כָּל שֶׁהוּא דִּין תּוֹרָה. וְאָסוּר לִגְנֹב דֶּרֶךְ שְׂחוֹק אוֹ לִגְנֹב עַל מְנָת לְהַחְזִיר אוֹ עַל מְנָת לְשַׁלֵּם הַכּל אָסוּר שֶׁלֹּא יַרְגִּיל עַצְמוֹ בְּכָךְ:
Whenever a person steals property that is worth a p'rutah or more, he transgresses a negative commandment, as Leviticus 19:11 states: "Do not steal." Lashes are not administered for the violation of this commandment, for one is obligated to give compensation. For the Torah requires a thief to compensate the party from whom he stole, whether he be a Jew or a gentile, an adult or a minor. The Torah prohibits stealing even the slightest amount. It is forbidden to steal as a jest, to steal with the intent to return, or to steal with the intent to pay. All is forbidden, lest one habituate oneself to such conduct.