If a manager of another department came to talk to you about moving (and you're at that large a company), there's a very good chance that the prospective manage

If a manager of another department came to talk to you about moving (and you're at that large a company), there's a very good chance that the prospective manager has already given your current manager a heads-up that you had that conversation, and may have even cleared it with him beforehand. Most companies of your size have a large HR department that has some serious procedures for all aspects of hiring, including interdepartmental hires. Plus, it's doubtful that your prospective manager would want to piss off your current one by going around him, seeing as it's in the prospective one's interest that he feels happy with the process (so that he doesn't block it in the future). If your current manager is a really good boss, he may have set this up to begin with because he sees you're the kind of guy the company want to employ, and that moving you somewhere else is preferable to losing you. Bottom line is don't worry about it - your boss is almost certainly waiting for you to have this conversation with him. Ask your prospective manager when you should talk to the current one about it (the answer is probably after the new one has filed the HR forms), and don't worry about finding a replacement - that's what you have an HR department for. You may be asked to set a reasonable transfer date to deal with knowledge transfer, but that's an issue for discussion between HR, your new manager, and your old manager. Given the size of your company, you're not the first person who has ever wanted to do an interdepartmental transfer; there's a procedure for it, so it's just a matter of kicking that into motion and following along. Your situation is unlike most of those discussed here (a multinational vs. a small business/start-up); don't get romantic notions about doing your personal bit to help out your manager or current team. There is a (likely large) HR department that exists to manage these things and set procedures, and it's unlikely your current manager even has much choice in terms of when and how you move departments.