2. A taxonomy of liability rules There are several ways in which legal systems can apportion liability between parties. Historically, a broad variety of liability rules has been developed by legal systems. Most early legal systems adopted liability rules that did not depend on the fault of the tortfeasor. This feature of early legal systems has been explained as instrumental to promoting appeasement between the parties and to avoiding cumbersome and controversial ascertainment of the subjective elements of a tort(Parisi, 1992 and 2001). Gradually, legal systems began to recognize fault as a viable basis for liability and in modern legal regimes strict liability is seen as an exception to the norm. Liability for accidents should arise only in the case of tortfeasor fault (including both negligent and intentional wrongdoing) We shall proceed with the presentation of some of the most common liability rules, starting from strict liability to simple negligence and more complex legal regimes. In our analysis we shall utilize the conventional terminology by which the injurer is defined as the individual who does not suffer harm in an accident and the victim as the individual who suffers such harm. In this survey, we shall focus on two-party accident There are two fundamental possibilities in a two-party accident The first occurs when both parties have to take precaution in order to avoid the accident (bilateral precaution). The second is given by situations in which either party ident(alternative precaution) In the second case, there is a waste of precaution cost if both parties take precaution, since one party's precaution would have been already enough. A particular and common case of alternative precaution is unilateral precaution As in alternative precaution, one party's precaution is enough to prevent the4 2. A taxonomy of liability rules. There are several ways in which legal systems can apportion liability between parties. Historically, a broad variety of liability rules has been developed by legal systems. Most early legal systems adopted liability rules that did not depend on the fault of the tortfeasor. This feature of early legal systems has been explained as instrumental to promoting appeasement between the parties and to avoiding cumbersome and controversial ascertainment of the subjective elements of a tort (Parisi, 1992 and 2001). Gradually, legal systems began to recognize fault as a viable basis for liability and in modern legal regimes strict liability is seen as an exception to the norm. Liability for accidents should arise only in the case of tortfeasor fault (including both negligent and intentional wrongdoing). We shall proceed with the presentation of some of the most common liability rules, starting from strict liability to simple negligence and more complex legal regimes. In our analysis we shall utilize the conventional terminology by which the injurer is defined as the individual who does not suffer harm in an accident and the victim as the individual who suffers such harm. In this survey, we shall focus on two-party accidents. There are two fundamental possibilities in a two-party accident. The first occurs when both parties have to take precaution in order to avoid the accident (bilateral precaution). The second is given by situations in which either party can take precaution and successfully avoid an accident (alternative precaution). In the second case, there is a waste of precaution cost if both parties take precaution, since one party’s precaution would have been already enough. A particular and common case of alternative precaution is unilateral precaution. As in alternative precaution, one party’s precaution is enough to prevent the