中文摘要：

当参与者的信息并非完全时，将出现委托代理问题。在委托代理问题相关研究中，通常假定委托人较代理人占有更多其他方面的资源，但由于种种原因，委托人不得不把工作交由他人去做。但代理人不会无偿替委托人做事．委托人必须向其支付报酬，当然明智的委托人也必定会对自己提供的报酬提出相应的要求。此时，必须求得信息不对称情况下．委托人为激励代理人朝着自己想要的方向努力而需要付出的额外成本，这就是委托代理问题希望解决的问题。而为了解委托人需要签订的契约，首先应知道委托人当前的处境，即其所面临的不对称信息的来源（主要包括隐匿行动和隐匿信息两种）及其引发的问题（逆向选择和道德风险），还有信息不对称问题发生的时序和其他限制条件。

英文摘要：

The principal-agent problem will be occurred when there is incomplete information or information asymmetry existing among the participants. In the research of principal-agent problem, it is usually assumed that, comparing to the agents, principals have more other resources; but influenced by all sorts of reasons, principals have to offer the job to others. The agents will not do that job for the principals without any payment; the principals have to pay for that; certainly, wise principals should impose some requirement suitable to their payment. At this time, we should understand, in the condition of information asymmetry, the extra cost for the principals to encourage the agents to do what they are required. That is the problem principal-agent problem will solve. To understand the contract principals should sign, we should first understand the current situation of the agents, namely the source of the asymmetric information （hiding behaviors and information）, the potential problems caused by that（adverse selection and moral hazard） and other limiting conditions.