除個別之債單純的聚合情形外，數人對單一債權人負擔給付義務時，多數債務人間即有內部分擔之問題，法律明文規定者如：可分債務、連帶債務、不可分債務等，學說及實務為免規範不足，另有協同債務、不真正連帶債務等概念，以茲處理，惟民法上關於連帶債務之規定，似僅係諸多可想像的計算方式之一，不應僅囿於此；此外，當多數債務人同時或各別與債權人間存有可抗辯事由時，其中一債務人對外關係之效力將影響內部分擔之計算，使問題更顯複雜！本文試圖整理多數債務人內部分擔問題相關理論脈絡，並特別著重於探討多數債務人間，倘有債務之免除與責任預先排除等事由發生時，內部分擔之計算上應為如何之處理。

In addition to the individual debts, all of the obligors needed to repay the debts to the single obligee. There were some problems among the obligors after one of the obligors repaid to the obligee, such as the divided responsibility, joint responsibility, and indivisible responsibility, etc. The theories and the practice avoided lacking of legal regulations; they developed some kinds of conceptions like coordination debts and unreal joint responsibility, etc. Nevertheless, it seemed one of the calculated ways about the joint responsibility in civil law. Moreover, the problems would be more complicate when there were defense reasons between the obligee and the obligors and one of the obligors' external relations affected the obligors' internal responsibility. This article attempts to systemize related theories about internal responsibility among the obligors. In particular, the focus is on the obligors who exempt from debts or responsibility in advance and then the obligors how to deal with internal responsibility.