There are over 160 central banks in the world,
and while their role has changed over the
years, primarily their duties include implementing
a monetary policy that provides employment,
currency stability and controlled inflation.
Their aim is a so-called "Goldilocks economy",
not too hot, not too cold. They do this
through managing interest rates, setting the reserve
requirement and acting as the lend of last
resort to the banking sector. Other responsibilites
include controlling the nation's entire money
supply and managing the country's foreign
exchange and gold reserves and the government's
stock register. They raise rates to slow growth,
and lower inflation. They lower rates 
to boost growth.
But when interest rates are almost zero, central
banks need to adopt different tactics,
such as pumping money directly into the financial
system. This process is known as quantitative easing.
Or QE. Quite simply, using money 
they printed, they buy bonds,
increase the amount of money in their financial system. This then encourages financial institutions
to lend more, allowing businesses and consumers
to spend more, boosting the economy.
After the financial crisis of 2007 to 2008, central 
bankers led change, but as of 2015
their ability to boost economic growth has stalled, 
and that has led many to question the role
of the central bank. Andrew Haldane from the Bank of 
England says: "Central bankers may need to accept that
their good old days – of adjusting interest rates to 
boost employment or contain inflation –
may be gone for good".
Economist Willem Buiter argues that ‘central banks have 
become the custodians of stability for financial markets,
a role for which they lack both democratic 
accountability and political legitimacy, ‘
And Mohamed El-Erian says: "We are rapidly nearing an 
inflection point where central banks will find their policy
approach increasingly and consequentially ineffective."
For now though, they remain the entity responsible 
for overseeing the monetary system for a nation,
or in the ECB's case, a group of nations.
