A Back-to-Back Letter of Credit - acts as an alternative to a Transferable Letter of Credit. 

It provides the mediators/first beneficiary/exporter the right to use the original Letter 

of Credit as a security in favor of the supplier, i.e., the secondary beneficiary.

 

Transferable Letter of Credit - it also acts as a credit document but is slightly different. 

Here the mediators / first beneficiary/exporter request the buyer to issue a Transferable 

Letter of Credit so that he can endorse it further to the supplier of the material, 

i.e., the secondary beneficiary.