Contract law governs the sale of real estate. Thus the Statute of Frauds (Uniform Commercial Code § 2-201), a principle of contract law, dictates that real estate transactions be in writing. Furthermore, since real estate transactions involve the sale of land, real property law also influences real estate law. For instance, the seller of property must show that that the title he or she is offering is marketable. Thus, the seller must prove that he or she owns title to the property and that no third party has an undisclosed interest in the property. However, real property is not synonymous with real estate. Real property only refers to land, while real estate also includes structures on the land.