THE Islamic religion forbids lending money at interest, a practice traditionally also frowned on by many Christian sects.
Islamic -- or Sharia -- law does not prohibit investments as such and many Islamic investors have been keen in recent years to shift money out of oil and other local markets.
Western companies, meanwhile, have been keen to tap into the vast wealth of not only oil-rich Arabian states but emerging economies in Indonesia and Malaysia.
To marry the two demands, the past decade has seen a major expansion of 'Islamic finance', including the Sukuk market.
Sukuk are the Islamic equivalent of bonds, used by companies and even countries when they want to raise money on the markets.
Traditional bonds are a type of IOU, explicitly a form of debt. That's where Sukuk differ -- Islamic bonds are set up to give the investor a share of ownership in an asset with a fixed share of profits and cash flows instead of fixed interest rates.
The ownership does not mean the Sukuk investor has any day-to-day involvement with the asset, and lapses when the money raised is paid back.
In practice, therefore, the relationship is just like that of a lender and borrower.
The market for Islamic finance is now global. News that the ESB could tap the sector today comes as Dublin's IFSC pushes to become a player in the market, joining not only Kuala Lumpur and Dubai but London and Istanbul.