The CISG only applies for the commercial sale of goods between parties whose business is located in different countries and both have signed the CISG. Is important to be clear the United Nations Convention on Contracts for the International Sale of Goods (CISG), only rules valid contract and in order to be valid a contract must comply with certain unique characteristics as general principle National Law determines usually if a contract is null or valid. The CISG is composed by 06 Parts distributed from Application scope Article 1 to entry into force Article 101.
The Contract under the CISG had three special characteristics:
• Firm Offer: "Until a contract is concluded an offer may be revoked if the revocation reaches the offered before he has dispatched an acceptance" [1] http://www.cisg.law.pace.edu.prx.proxywebsite.co.uk/cisg/biblio/mather2.html CISG Article 16 has the common law rule that offers are revocable even in oral and the the acceptance is effective when it reaches the offeror.
• The Mailbox Rule: "A statement made by or other conduct of the offeree indicating assent to an offer is an acceptance. Silence or inactivity does not in itself amount to acceptance." [2] http://www.cisg.law.pace.edu.prx.proxywebsite.co.uk/cisg/text/e-text-18.html CISG Article 18 has introduce the idea that major responsibilities in case of lost communication is on the parties who is in the top position to chose superior communication channels besides that silence is not acceptance unless have been jurisprudence.
• The Battle of the Forms:"A reply to an offer which purports to be an acceptance but contains additions, limitations or other modifications is a rejection of the offer and constitutes a counter-offer" CISG Article 19.Basically what it means is all the new terms that have not been altered becomes part of the contract the hitch comes when some terms had changed (rejecting the old) that's mean that have been a counteroffer based solemnly in the terms changed the rest remain the same within the same contract and this contract is accepted unless the offeror object the new term. The CISG is very specific that changes to: (price, payment, quality and quantity, place and time of delivery, extent of one party's liability to the other, settlement of disputes among others) constitute not acceptance of the terms and therefore a new terms are in place, if those new term don't match there is not contract. The legal system has two different approaches to resolves problems under the battle of the forms.