Abstract: The invention allows electronic initiation of payments and provision of payment assurance through an initiation intermediary logically located between the buyer and seller and the buyer's and seller's banks. Electronic messages between parties using the system embodying the invention are governed by a set of rules, known as a Rulebook, that defines the roles, obligations and liabilities of all the players, and which provides the legal framework for the creation of the payment initiation mechanism to facilitate B2B Internet based commerce. Transaction terms, including payment terms, are first negotiated between the buyer and seller. An initiation message comprising a payment instruction, optionally a payment assurance request, and/or commercial transaction data is sent from the buyer, for example through the seller's web site, to the payment initiation intermediary. Commercial transaction data is held at the intermediary and a payment instruction sent to the buyer's bank.