In this Essay, we introduce our planned ten-part series that provides the first comprehensive examination of the offices and officers of the Constitution. This series will explain the original public meaning of twelve clauses of the Constitution that refer to six categories of offices and officers. First, the phrase "Officers of the United States" refers to appointed positions in the Executive and Judicial Branches. Second, the phrase "Office ... under the United States" refers to appointed positions in the Executive and Judicial Branches and also includes non-apex appointed positions in the Legislative Branch. Third, the phrase "Office under the Authority of the United States" includes all "Office[s] . . . under the United States," and extends further to include a broader category of irregular positions. Fourth, the phrase "Officer" of "the Government of the United States" refers to the presiding officers identified in the Constitution. Fifth, the word "Officer," as used in the Succession Clause, refers to those who hold "Office . . . under the United States" and those who are "Officer[s]" of "the Government of the United States." Sixth, the phrase "Office or public Trust under the United States" encompasses two categories of positions: "Office[s] . . . under the United States" and "public Trusts under the United States." The former category includes appointed positions in all three branches; the latter category includes federal officials who are not subject to direction or supervision by a higher federal authority in the normal course of their duties.