Many folks keep their funds in joint accounts with friends or relatives. Though some may do so intentionally, knowing full well that the entire asset will pass to the survivor on the account at their death,others may not be fully aware of the implications of such an arrangement. Hyman Darling Esq. of the  Massachusetts law firm of Bacon and Wilson has written a cautionary primer explaining the basics about joint accounts which I have republished for you here.  I would add, however, that it is likely that the suggestion that instructions in your will may be used to qualify the intent of a joint account may not wash all that well in New York. In fact, if all of the assets of a New York resident are in a joint account, it is likely that his or her will won’t even be probated. Therefore, pay specific attention to what you need to do if it is not your intention for your co-depositor to have these assets after you die. When in doubt, consult your lawyer. He or she will offer better guidance than the platform officer at your bank.