Separate. Some companies are big enough to have a tax division and an investment division. There are also some professionals who claim to be able to do everything. Generally, in almost every situation, you should have three people, one for each role. For example, as a financial planner, I am not an accountant and I am not an attorney, and everything I say about those two fields is not final and should be checked against an expert in that field. That said, I often consult together with accountants and attorneys (and often insist on it) and am very familiar with what they do, what it costs, and what structure may be best in a given situation.