I do solemnly swear

that I will support and defend the Constitution of the United States against all enemies, foreign and domestic;

that I will bear true faith and allegiance to the same;

and that I will obey the orders of the President of the United States

and the orders of the officers appointed over me, according to regulations and the Uniform Code of Military Justice.

So help me God

The founders decided to require an oath for federal and state officials—absent a religious test—in the Constitution, but the specifics—such as the wording of the oath—were left to the First Congress (1789–1791). In its first act, Congress specified the wording: “I, A.B. do solemnly swear or affirm (as the case may be) that I will support the Constitution of the United States.” This oath was used for all federal officials except the President, whose oath was prescribed specifically in the Constitution (Article II, section 1, clause 8). 

The form of the oath has changed several times since that first act of Congress. During the Civil War, Congress mandated that the oath bar from office anyone who had been disloyal to the Union. Eventually, those elements of the “iron-clad” oath were dropped during revisions in 1868, 1871, and 1884. The oath used today has not changed since 1966 and is prescribed in Title 5, Section 3331 of the United States Code. It reads: “I, AB, do solemnly swear (or affirm) that I will support and defend the Constitution of the United States against all enemies, foreign and domestic; that I will bear true faith and allegiance to the same; that I take this obligation freely, without any mental reservation or purpose of evasion, and that I will well and faithfully discharge the duties of the office on which I am about to enter. So help me God.” In contrast to the presidential oath, where it’s used only by tradition, the phrase “so help me God” has been part of the official oath of office for non-presidential offices since 1862.