In essence, this means that an outside actor, the government, the regulator or the system operator, needs to step in to ensure that such external costs are not overproduced and are correctly internalised. Economic theory has devised a number of corresponding instruments, including standards and technical regulations, pollution taxes, new markets such as emissions trading, better information and research, as well as an overall strengthening of the legal system. Overcoming the knowledge gap is also part of moving towards sustainable electricity systems.