to use claims-made policies to push a substantial amount of risk back to insureds, and claims-made coverage was the subject of extensive litigation in several countries throughout the 1970s, 1980s, and 1990s. This led to important decisions of the U.S. Supreme Court in 1978 and 1993 and of the Supreme Court of Canada in 1993. Retained limits and SIRs One way for businesses to cut down their liability insurance premiums is to negotiate a policy with a retained limit or self-insured retention (SIR), which is somewhat like a deductible. With such policies, the insured is essentially agreeing to self-insure and self-defend for smaller claims, and to tender and demand a defense only for liability claims that exceed a certain value. However, writing such insurance is itself risky for insurers. The California Courts of Appeal have held that primary insurers on policies with a SIR must still provide an "immediate, 'first dollar' defense" (subject, of course, to their right to later recover the SIR amount from the insured) unless the policy expressly imposes exhaustion of the SIR as a precondition to the duty to defend. Types In many countries, liability insurance is a compulsory form of insurance for those at risk of being sued by third parties for negligence. The most usual classes of mandatory policy cover the drivers of motor vehicles (vehicle insurance), those who offer professional services to the public, those who manufacture products that may be harmful, constructors and those who offer employment. The reason for such laws is that the classes of insured are deliberately engaging in activities that put others at risk of injury or loss. Public policy therefore requires that such individuals should carry insurance so that, if their activities do cause loss or damage to another, money will be available to pay compensation. In addition, there are a further range of perils that people insure against and, consequently, the number and range of liability policies has increased in line with the rise of contingency fee litigation offered by lawyers (sometimes on a class action basis). Such policies fall into three main classes: Public liability Industry and commerce are based on a range of processes and activities that have the potential to affect third parties (members of the public, visitors, trespassers, sub-contractors, etc. who may be physically injured or whose property may be damaged or both). It varies from state to state as to whether