The Thai criminal justice system is fraught with problems of inefficiency in many parts of its process. Each year the courts receive many more cases than they can decide, leaving a growing backlog of undecided cases. The number of imprisoned convicts is roughly 170 percent the carrying capacity of prisons. However, these overloads are not the result of a lack of resources. By international standards, the Thai criminal justice system consumes relatively more resources in terms of budget and personnel than many other countries. There are many ongoing initiatives to streamline the criminal procedures. For example, the court has introduced a system of continuous case hearings. The Ministry of Justice has promoted the use of alternative dispute resolution, “community justice” and “restorative justice.” Useful as they are, these initiatives have so far been unable to significantly reduce the inefficiencies in the criminal justice system. We argue that, unless the system is reformed to be more efficient, accessibility and fairness would be of limited value. As the saying goes: “justice delayed is justice denied.” We argue that an economic analysis can provide fresh insights into the problem and offer new perspectives for possible solutions. We assume that individuals are rational in the sense that they are forward looking and attempting to maximize their own interests. From this perspective, people commit criminal offenses if they expect the net benefits from them to exceed the net benefits they could obtain by performing other activities. Net benefits related to a crime are defined as benefits from the crime minus the costs in conducting it and the costs arising from being prosecuted and punished. Similarly, a rational injured person will file a criminal lawsuit if he expects the net benefits from it to exceed the net benefits he could obtain from other activities, including filing a civil lawsuit. As criminal sanction involves the use of public resources, if a dispute that is private in nature is allowed to be settled criminally, the plaintiffs would have an incentive to overuse the justice system by initiating more lawsuits than necessary since they would not have to bear the full cost of their actions. Another key major insight of the economic approach is that monetary sanctions such as fines are superior to non-monetary ones such as imprisonment in many ways. Aside from relatively small collection costs, the social cost of fines is almost zero, as they are just transfers from the convicted offenders to the public. Fines also have another advantage over imprisonment in that, while still furnishing deterrence effects, they do not deprive the convicted offenders of freedom and attach social stigma to them. As a result, they do not have the negative effects of excluding the offenders from current and future labor market and disrupting economic activities. On the other hand, the cost of imprisonment can be very high, as it comprises the sum of the earnings foregone, the value placed on the restrictions on consumption and freedom, and the social costs of stigmatization. Based on such insights, we hypothesize that the inefficiencies of Thailand’s current criminal justice system are a result of two major problems: (a) systematic biases toward criminal proceedings over civil ones, and (b) the underutilization of monetary sanctions and the overutilization of imprisonment. To test our hypotheses, we analyze the Thai legislations and sampled court cases decided during 2003-2008. The analysis confirms that the Thai legal system indeed prefers criminal sanctions to civil ones. In particular, it is found that there are over 350 legislations that provide criminal sanctions against prohibited actions. Many of them are related to disputes between private parties over private matters such as defamation and the use of bounced cheques. We also found that even though almost all statutes provide judges with a choice of imposing imprisonment or fines, or both, on convicted offenders, imprisonment has been the predominant mode of sanction by the court. Fines are used only in cases involving minor criminal offenses, such as gambling, or in combination with suspended imprisonment. Based on the sampled court cases, we construct a model to estimate the costs borne by the state in conducting criminal proceedings. We found that it costs averagely about 76,600 Baht to settle a criminal case accepted by the Court of First Instance. This includes the costs to finance the operation of the police, prosecution, all levels of courts, prisons and correction facilities. If the costs borne by private parties, such as lawyer fees and their opportunity costs, are also included, the total cost is likely to become much higher. Based on the model, we estimate the potential cost savings that can be achieved by the following six reform proposals that have been suggested: 1. Decriminalizing certain mala prohibita offences. In particular, we estimate the cost saving arising from decriminalizing the use of bounced cheques and defamation. We also estimate the savings arising from replacing criminal sanctions with administrative ones to sanction violators of transportation, building and service provision regulations. 2. Requiring the parties to attempt to settle their disputes through mediation. The estimation assumes a success rate of 50 percent, as indicated by a previous study. 3. Disallowing plaintiffs to file criminal cases directly to the court without an approval from a public attorney. 4. Requiring the court to conduct preliminary examination of the cases filed by public attorneys before accepting them. 5. Replacing short-term imprisonment (less than 1 year) with monetary fines. 6. Abolishing the discretion of judges and the public attorneys to allow a case to be appealed to the Supreme Court.