Inclusion of Ts&Cs
Serbian law requires that Ts&Cs need to be agreed between the parties in order for them to be considered as contracts or as a part of a contract (same condition as in concluding any other contract, primarily meeting of the minds). The agreement can be express, e.g. in a framework agreement, but also implied, e.g. reference to one's Ts&Cs. A reference to specific Ts&Cs in offer or order documents is generally sufficient (provided that such offer or order documents fulfil other conditions necessary for conclusion of any other contract) unless there is a Battle of Forms situation.
Ts&Cs need to be provided to the other contracting party in an appropriate manner (i.e. it is not enough to state that Ts&Cs will be sent upon request) and incorporated in the contract itself or referred to; the party which was presented with an offer needs to be familiar (or should have been familiar) with the Ts&Cs in order for them to be considered a part of the contract.
From a Serbian law perspective, under the CISG, the same situation as under national law applies.
Battle of Forms
Under Serbian law, the following distinction applies: Knock-Out Rule regarding mandatory provisions. Otherwise, Last-Shot Rule can be applied (discretion of the court depending on concrete case).
From a Serbian law perspective, under the CISG, the same situation applies as under national law.