Question: For centuries, seforim were printed with rabbinic haskamos (approbations) prohibiting others from reprinting the sefer during a specified number of years, often with a curse (nidui or cherem) attached. What is the basis for this practice?

Answer: Many based the haskamos on hasagas gevul (encroachment). In situations where not applicable, other reasons were advanced: 1) A takanas chachamim (rabbinical enactment) of the Sages of each generation to enable the creator profit. 2) Mutual agreement of the publishing trade. 3) To strengthen doers of mitzvah, so that shouldn't be concerned about losses. 4) As an established practice without dissent that became entrenched.

According to the opinion of many achronim and contemporary poskim that halacha recognizes ownership of IP, we can explain the need for haskamos in a number of ways: 1) To strengthen the prohibition in people's eyes. 2) For publishers of old works over which there is no ownership. 3) Not every new work is sufficiently a "new mental creation" to be considered IP. 4) On account of the mitzvah to teach Torah, ownership in Torah IP may be limited to a certain degree.

(See Emek Hamishpat, Zechuyos Yotzrim, intro. 21; ch. 17-20)