The U.S. does not have an inheritance tax. Thus, any inheritance you receive as a beneficiary is tax-free to you (assuming relevant estate taxes have been paid). In limited instances the U.S. government may attach beneficiary inheritances where the estate were subject to U.S. estate tax and failed to pay prior to distribution to the heirs.
However, should you ever inherit a tax-deferred account such as a 401(k) or pension account, any distributions you take would be subject to income tax the same as if the decedent owner took a distribution. This is called income in respect of a decedent (IRD). If you inherit tax-deferred accounts seek competent tax counsel as you have significant choices to make regarding titling of the accounts and required distributions. Of course any investment income generated by the inherited funds (once you receive it) would be subject to normal taxation.
Except for items of IRD (see above) your cost basis in inherited property will generally be equal to the fair market value as of the date of the decedent's death (unless an estate tax return is filed and the executor chooses an alternate valuation date). Accordingly, if you sell the property you will only be taxed on post-death appreciation. The heirs are automatically presumed to have held any inherited property more then one year, thus entitling you to long-term capital gains rates if you sell. Thus, the maximum Federal tax rate on gains on the sale of inherited property is15% (5% if the gain would otherwise be taxed in the 10% or 15% regular tax brackets).
Some states do tax inheritances however. If you tell me what state your a resident of and the state of residence of the decedent, I can indicate whether you may have a state inheritance tax issue.
Because it is impossible for me to identify and consider ALL the relevant facts, this advice is not intended or written to be used for the purpose of avoiding penalties, and cannot be used for that purpose.