What is a debt restructuring?

The aim of any restructuring (also sometimes called a workout) is to rearrange the debtor’s financial commitments so that it is able to service its restructured debts and survive as a going concern. It is important to note that this is a consensual process and is not undertaken under the supervision of a court or other supervisory body - therefore, it is important the all creditors are involved.  

If it’s voluntary, how does it work?