Trust, consisting of both rational and emotional elements, plays a special role in society, in regard to cultural, moral, psychological and biological issues, and therefore the research about trust embodies multiple disciplines and multiple dimensions. According to different standards, there are various classifications of trust. The trust of law can be defined as an important one of system trust. Besides, from an abstract perspective, trust and law can be seen as formal and informal systems respectively, to enhance social integration and interaction, and they can work together well. In law, especially in private law, there are some mechanisms aiming at protecting trust, such as fiduciary duty in common law and good faith (bona fides) in continental law. The former can be thought of as a standard of conduct, while the latter is a blanket clause, and they can be studied in a comparative way.