Finally, trust funds permit the bank and donors to support innovative regional and global projects that do not fit with the IBRD/IDA country focused allocation system. The bank has highlighted how trust funds allow it to expand its global partnerships for global public goods, emergency response, novel focuses (like gender), and, crucially, the control of communicable diseases.4 10 12 15 Several health trust funds have also allowed the bank to fundraise in new ways or to pilot new financing mechanisms. For instance, the bank has used trust funds to incentivise IDA loans for maternal and child health (see paper 4 of this series on the Global Financing Facility28), to encourage donors to buy down IDA loans for countries investing in polio control,29 30 and to provide Wall Street based insurance against future global pandemics (see paper 5 of this series on the Pandemic Emergency Financing Facility31). Similarly, trust funds supporting health results based financing have enabled the bank to pilot performance based financing at a village level before deciding whether to apply this strategy nationwide.4