Art. 10 CISG
For the purposes of this Convention:
(a) if a party has more than one place of business, the place of business is that which has the closest relationship to the contract and its performance, having regard to the circumstances known to or contemplated by the parties at any time before or at the conclusion of the contract;
(b) if a party does not have a place of business, reference is to be made to his habitual residence.
The Secretariat Commentary on Art. 9 of the 1978 New York Draft, predecessor to Art. 10 CISG, gives insight into the drafters' unterstanding on the eve of the 1980 Vienna Diplomatic Conference.
Overview of case law on Art. 10 CISG: UNCITRAL Digest
The UNCITRAL Digest on the CISG can be used as a starting point to discover the relevant case law on this article.