Nauru has become the 189th member of the International Monetary Fund and the World Bank.
The World Bank says Nauru faces challenges in sustaining growth and ensuring fiscal and debt sustainability over the medium term - challenges faced by many other Pacific countries.
By joining the World Bank, Nauru gains access to financial and technical support and special expertise in issues such as water, sanitation, disaster risk management and climate change mitigation.
The IMF says Nauru can benefit from the crisis lender's advice on managing government finances and monetary policy.
Nauru applied for membership in the Washington-based organisations in April 2014.