US municipal bonds were traditionally thought of as among the most secure debt around, but a perfect storm hit the market last year, leading to a frozen municipal credit market.
The Obama administration responded with its Build America Bond (BAB) programme, which has enabled state and local governments, which mostly issue tax exempt bonds, to tap into the larger and more liquid taxable bond market. This was a dramatic move that has introduced new opportunities and risks to international investors.

FTFM 

