In 1998, resolution number 115/98 of the Portuguese Minister Council started a national initiative of electronic commerce. The Portuguese information society should adopt a new business model based on the electronic commerce, bringing to the Portuguese economical structure a renewed competitive capability in order to keep up with other European and global business partners. The European focus on process optimization led more recently to the 2001/115/EC directive. With the intent of simplifying the conditions applicable to invoicing in terms of VAT, by 2005 the Portuguese government has started a renewed initiative that had as a primary objective to provide the means necessary to implement electronic invoicing in the public administration and in Portuguese enterprises. This dissertation focus on standards and formats recommended for messages, storage, security and transport mechanisms for commercial documents. Using Microsoft's BizTalk Server, we aim to show how this technology can answer to every aspect of an electronic invoicing solution, from integration with existing systems, compliance with message formats and security, to overall performance and high level of extensibility.