I have been separated from my husband for the last three years. We split custody of our only son; hwever, there is no legal decree awarding either of us legal custody. We are both residents of Maryland and we also equally share the financial obligations for rearing our son. Our arrangement is one where neither of us has custody of the child more than the other parent. My question, can we both claim our son or should we alternate claiming him until we complete the legal process of a separation or divorce? We both claim separate status on our files.

Only one person can claim a person as a dependent at a time, so no - you cannot both claim him in the same year. You can alternate years, if you are on good terms with your ex I suggest you work out some sort of deal like that. Alternatively, if one of you is in a higher tax bracket the exemption is worth more to that person - perhaps the higher income person could negotiate a sort of "buy out" of the other parent's right to claim the child. Again, this will only work if you're on good terms.

If you can't reach an agreement with your ex, and you both try and claim the child, the IRS will resolve the dispute in favor of (1) who the child resided with the most - in this case that's a tie, then (2) who has the higher AGI.