The topics of “F-4” registration and the “10% Rule” have attracted a great deal of attention recently, being covered by several memoranda in a leading Japanese financial publication.1 Japanese companies are frequently surprised that a business combination entered into solely among Japanese companies might need to be registered with the U.S. Securities and Exchange Commission (the “SEC”) before the transaction can be approved by target shareholders. As is often the case with hot topics like this, questions and confusion abound. This memorandum has been prepared to help answer many of these questions, clear up some of the confusion and to explain the F-4 registration process and its consequence for Japanese companies.