If you are entitled to a "renter's credit" on your state tax return and in order to claim the credit you are required to have a credit certificate of some type, then it's the landlord's obligation to provide you that document. For most states they have until Jan 31st to have it post marked and in the mail. So it's possible you just need to wait.
If not received by the end of the first week of Feb, then contact your landlord.