にあたって

1. 1On the occasion of, or at the start of, a formal event, typically introducing a statement or greeting.Ex. 1
2. 2When about to undertake something significant, introducing preparations or considerations made beforehand.Ex. 2

A formal expression used in speeches, greetings, business documents and announcements about significant events such as openings, new ventures, moving abroad or starting a job. It frames the occasion as a turning point that calls for preparation, resolve or a formal statement. For ordinary, everyday situations, a plain 時に is more natural.

• にあたりN2「にあたり」 is the continuative (ren'yō-chūshi) form of 「にあたる」 and means the same as 「にあたって」, so the two are generally interchangeable. However, it is more formal and stiff, and in speeches the even more polite form 「にあたりまして」 is often used.
• に際してN2「に際して」 has the same attachment patterns and register as 「にあたって」, and the two are interchangeable when giving speeches or making formal statements. However, it focuses on the moment the occasion itself arrives and does not highlight preparation made for it; in writing, the pause form 「に際し」 is also used.
• 〜に先立ってN2「に先立って」 only indicates doing preparations or holding ceremonies in advance, before the event begins, and does not refer to the event itself; when talking about advance preparation, it can be swapped with 「にあたって」. To modify a noun, use 「に先立つ」 or 「に先立っての」 + noun.
• 際にN3「際に」 simply indicates a time or occasion, is not limited to major events, and can be used in contexts such as procedural explanations; it can attach to the た-form to look back on past events, and requires 「の」 after a noun. When used for major events it is often interchangeable with 「にあたって」, but it lacks the nuance of solemnly facing the occasion and setting about preparations.
• 折にN1「折に」 refers broadly to some occasion or opportunity; it can take the た-form to describe past events, and often appears as 「お/ご〜の折には」 to make invitations or requests. When describing preparations, it does not emphasize the sense of facing the matter and acting on it as strongly as 「にあたって」 does.
• をきっかけにN2「をきっかけに」 indicates that something becomes a trigger or cue that leads to a change or new action, whereas 「にあたって」 refers to giving a speech or making preparations when facing an important occasion and carries no sense of cause, so the two cannot be interchanged. The former is neutral in register, and a verb must first take 「の」 before it.

にあたり is a stiffer, more written variant of にあたって. に際して is very close and equally formal, and it can also introduce greetings or preparations for an event, but にあたって more strongly suggests facing an important undertaking with preparation or resolve. 〜に先立って stresses doing something beforehand, 際に is a more neutral 'when', 折に is a polite 'on the occasion/opportunity', and をきっかけに marks a trigger that leads to a change rather than preparation for an occasion.