I am an American citizen and I own some property outside of the US. I am thinking of selling my property. What are the tax laws?

You must report the sale on Schedule D and pay taxes on the capital gain, if any.

You treat the sale in the same way as any property in the U.S.
If you paid taxes in a foreign country on the capital gains from the sale of property, you will file Form 1116 to claim foreign tax credit.