Ribbis is the prohibition of charging interest on loans according to Jewish Law. This prohibition is derived from several passages in the Torah that forbid charging interest to a fellow Jew. This prohibition is extensive, encompassing not only loans of money but also loans of any item that is usually sold by measure or number. There are certain leniencies and structures like "heter iska" that allow business transactions to function within the bounds of this prohibition.

Messenger Borrowing for a Goy A Jew can serve as an agent for a Goy and secure an interest loan for him from a Jew lender, on condition that the lender relies only on the collateral or contract provided by the Goy and none of the responsibility falls upon the Jewish agent. The Jewish agent can even transfer the actual interest money from the Goy to the lender, as long as the Jewish lender accepts full responsibility upon himself for anything that might happen during the transit of the agent bringing the payment or returning the collateral.[2] A Jew who takes an interest free loan from a Jewish lender and needs more time to pay him back, can instruct the lender to take a loan with interest from a Goy using the collateral he gave him, and he the original borrower will pay the loan and interest back to the Goy. This is permissible as long as the Goy lends solely based on the value of the collateral.[3] Messenger Borrowing from a Goy A Jew can serve as an agent for another Jew and secure an interest loan for him from a Goy lender, on condition that the lender relies only on the collateral or contract provided by the final Jewish borrower and none of the responsibility falls upon the Jewish agent.[3] The Jewish agent can even transfer the actual interest money from the Goy to the lender, as long as the Jewish lender accepts full responsibility upon himself for anything that might happen during the transit of the agent bringing the payment or returning the collateral.[2] Taking over the Loan of a Goy A Jewish lender who has provided a loan to a Goy, backed by a collateral and carrying a fixed monthly interest rate, may choose to recover his money ahead of time. He can achieve this by borrowing an equivalent amount from another Jewish individual. The collateral from the original loan is then transferred to this new lender and he is entitled to collect the monthly interest from the Goy borrower until the loan is repaid. However, if the initial Jewish lender already established a set amount for the principal and interest for the entire duration of the loan, then the whole amount is considered as already possessed by him and it is prohibited for him to pass this interest to the 2nd Jewish lender, because it is as if he paid the interest from his own pocket.[4] Guarantors Guarantor for another Jew borrowing from a Goy with interest: - Guaranteeing the loan is permissible, if according to local law, the Goy lender cannot demand payment from the guarantor unless the Jewish borrower is unable to repay. - However, if local law allows the Goy lender to initially collect from the guarantor, guaranteeing the loan is prohibited. It is viewed as if the guarantor is effectively borrowing from the Goy lender and then re-lending it to the Jewish borrower. Guarantor for a Goy borrowing from another Jew with interest: - Guaranteeing the loan is permissible if according to local law, the Jewish lender can't collect payment from the guarantor unless the Goy borrower is unable to repay. - However, if local law allows the Jewish lender to initially collect from the guarantor, guaranteeing the loan is prohibited. It is viewed as if the guarantor is effectively borrowing with interest from the Jewish lender. An exception exists if the guarantor only assures the principal loan and not the interest, in which case, it is permissible.[1]

[1] Kitzur Shulchan Aruch 65:24 [2] Kitzur Shulchan Aruch 65:25 [3] Kitzur Shulchan Aruch 65:26 [4] Kitzur Shulchan Aruch 65:27