Abstract: The present study aims to analyze a specific instrument of the procedures for determining the tax debts: the invoice. This instrument, supporting document, is extremely present in contractual arrangements between professionals and generates legal effects primarily on a fiscal level. On the legal nature of this document, its probative force and its effects, we will point to a range of nuances both from a tax perspective and from the practice of litigation between professionals. Equally, the study will look at contemporary systems for issuing and communicating invoices in electronic environments and the effects of these invoices.

Keywords: invoice, online, electronic, copy, original