The battle of forms (contract law) in Belgium

National Law
In Belgium, the Ts&Cs will only be binding for the parties if they reached an agreement about them. An agreement requires that the Ts&Cs are known by the parties (or ought to be known) and that the parties gave their consent to be binding by the Ts&Cs. The consent can be express, e.g. in a framework agreement, but also implied, e.g. by not making any reservation when receiving a copy of the Ts&Cs. A mere reference to one‘s Ts&Cs via a website or via a chamber of commerce is not sufficient.

CISG
From a Belgian law perspective, under the CISG, the same situation as under national law applies.

National Law
If the parties have informed each other about their respective Ts&Cs and have not rejected the other party’s Ts&Cs, both sets of Ts&Cs will apply. In case of contradiction between respective stipulations, no less than 3 theories exist in case law: (i) the nullity of the respective stipulations (i.e. the Knock-Out Rule), (ii) the terms & conditions first communicated prevail (i.e. the First-Shot Rule), (iii) the terms & conditions most recently communicated prevail.
The Knock-Out Rule with the nullity of the respective stipulations is most commonly applied by the Belgian courts. Statutory law will be applicable.

CISG
From a Belgian law perspective, under the CISG, the same situation as under national law applies.

CMS DeBacker
Chaussee de La Hulpe 178
1170 Brussels
Belgium