Letter of Undertaking is abbreviated as LUT. The Letter of Undertaking is a document submitted by the exporter in order to export goods or services without the payment of taxes. All registered tax payers who export the goods or services have to furnish Letter of Undertaking (LUT) in GST RFD-11. In case the LUT is not filed, the exporter may export by payment of IGST and then claim the refund of tax paid. There are two ways possible to export under GST, one is export with payment of GST and second is export without payment of GST. To chose second option, you need to file the bond or LUT with the tax department stating that you shall fulfill all the export requirements.