This chapter provides insights into the law on contract formation in Japan. The Japanese approach is traditional, requiring an agreement which, in turn, normally requires an offer and matching acceptance, according to the mirror image rule. Once offers become effective, the 1898 Japanese Civil Code severely restricts their revocability. This is in tune with the mostly German origins of Japanese contract law. However, the drafters of the Code deliberately followed the common law in one respect: the offeree’s acceptance becomes effective as soon as it is dispatched. This is highly controversial and in 2001 was abolished for acceptances by electronic means. Ongoing major reform of Japanese contract law will probably extend this solution to all contracts. Japanese law has no doctrine of consideration and has traditionally eschewed formal requirements as a prerequisite for the validity or enforceability of contracts. More recently, formalities have been introduced, first, for certain consumer contracts, then for contracts of suretyship. A particular feature of Japanese law pertaining to contract formation is the strong duty to negotiate in good faith.