Casual observers of the use of signing statements likely would believe they are a new phenomenon. This is a reasonable belief given the lack of scholarly information available but, that belief couldn't be further from the truth. The first signing statement is traced back to President James Monroe in 1822. Signing statements are either rhetorical or substantive. Rhetorical statements are little more than press releases attached to a bill. Substantive statements are used to interpret a bill, to make assertions regarding the bill's constitutionality, or sometimes both. These statements are used to influence the judicial branch, to influence congress, and to direct the executive branch. Many authors believe that using signing statements to attempt to influence the other branches is a violation of the separation of powers doctrine. This thesis asserts that the key element in the constitutionality of the use of any signing statement is the direction given to the executive branch. When the direction is to enforce the bill in a manner that is contrary to the intent of congress the president is essentially rewriting the law and taking on a legislative capacity. This can be done either by claiming the bill is unconstitutional or offering an interpretation of terms or provisions that clearly differs from the intent of congress. This thesis offers a plan for presidents to follow to ensure that their use of substantive signing statements does not exceed their constitutional powers.