The jurisdiction of the United States Senate Select Committee on Ethics is derived from the Constitution and authority granted under law and Senate Rules.
Article I of the U.S. Constitution – U.S. Const. art. I, § 5, cl. 2
Article I of the U.S. Constitution states that: “Each House may determine the Rules of its Proceedings, punish its Members for disorderly Behavior, and, with the Concurrence of two thirds, expel a Member.”
Preamble to Senate Resolution 266 – S. Res. 266, 90th Cong. (1968)

The Preamble to Senate Resolution 266, by which the Senate Code of Official Conduct was first adopted, provides that:

“(a) The ideal concept of public office, expressed by the words, ‘a public office is a public trust,’ signifies that the officer has been entrusted with public power by the people; that the officer holds this power in trust to be used only for their benefit and never for the benefit of himself or of a few; and that the officer must never conduct his own affairs so as to infringe on the public interest. All official conduct of Members of the Senate should be guided by this paramount concept of public office.

(b) These rules, as the written expression of certain standards of conduct, complement the body of unwritten but generally accepted standards that continue to apply to the Senate.”

Senate Resolution 338 – S. Res. 338, 88th Cong. (1964)

Section 2a of Senate Resolution 338 provides that: “It shall be the duty of the Select Committee to—(1) receive complaints and investigate allegations of improper conduct which may reflect upon the Senate, violations of law, violations of the Senate Code of Official Conduct and violations of rules and regulations of the Senate, relating to the conduct of individuals in the performance of their duties as Members of the Senate, or as officers or employees of the Senate, and to make appropriate findings of fact and conclusions with respect thereto;

(2)(A) recommend to the Senate by report or resolution by a majority vote of the full committee disciplinary action to be taken with respect to such violations which the Select Committee shall determine, after according to the individual concerned due notice and opportunity for a hearing, to have occurred; (B) pursuant to subparagraph (A) recommend discipline, including—(i) in the case of a Member, a recommendation to the Senate for expulsion, censure, payment of restitution, recommendation to a Member’s party conference regarding the Member’s seniority or positions of responsibility, or a combination of these; and (ii) in the case of an officer or employee, dismissal, suspension, payment of restitution, or a combination of these;

(3) subject to the provisions of subsection (e), by a unanimous vote of 6 members, order that a Member, officer, or employee be reprimanded or pay restitution, or both, if the Select Committee determines, after according to the Member, officer, or employee due notice and opportunity for a hearing, that misconduct occurred warranting discipline less serious than discipline by the full Senate;

(4) in the circumstances described in subsection (d)(3), issue a public or private letter of admonition to a Member, officer, or employee, which shall not be subject to appeal to the Senate;

(5) recommend to the Senate, by report or resolution, such additional rules or regulations as the Select Committee shall determine to be necessary or desirable to insure proper standards of conduct by Members of the Senate, and by officers or employees of the Senate, in the performance of their duties and the discharge of their responsibilities;

(6) by a majority vote of the full committee, report violations of any law, including the provision of false information to the Select Committee, to the proper Federal and State authorities; and

(7) develop and implement programs and materials designed to educate Members, officers, and employees about the laws, rules, regulations, and standards of conduct applicable to such individuals in the performance of their duties.”

Senate Resolution 400 – S. Res. 400, 94th Cong. (1976)
Senate Resolution 400 authorizes the Senate Select Committee on Ethics to investigate unauthorized disclosures of intelligence information by a Member, officer, or employee of the Senate and to report to the Senate on any substantiated allegation.
Franked Mail – 39 U.S.C. §§ 3210-3220
39 U.S.C. §§ 3210-3220 authorizes the Senate Select Committee on Ethics to provide guidance and promulgate rules regarding the frank. The Committee may investigate complaints involving a violation of the statute.
Ethics in Government Act – 5 U.S.C. § 13101 et seq. (Adopted as Senate Rules 34 and 36)
The Ethics in Government Act designates the Senate Select Committee on Ethics as the “supervising ethics office” for the Senate and charges the Committee with duties and responsibilities for financial disclosure reports and outside employment with respect to Members, officers, and employees of the Senate.
Foreign Gifts and Decorations Act – 5 U.S.C. § 7342
The Foreign Gifts and Decorations Act (FGDA) designates the Senate Select Committee on Ethics as the “employing agency” for the Senate and charges the Committee with administering the provisions of the FGDA with respect to Members, officers, and employees of the United States Senate.
Gifts to Superiors – 5 U.S.C. § 7351
5 U.S.C. § 7351 designates the Senate Select Committee on Ethics as the “supervising ethics office” for the Senate and charges the Committee with administering the statutory prohibitions on Members, officers, and employees of the Senate giving gifts to an official superior or receiving gifts from employees with a lower salary level.
Gifts to Federal Employees – 5 U.S.C. § 7353
5 U.S.C. § 7353 designates the Senate Select Committee on Ethics as the “supervising ethics office” for the Senate and charges the Committee with administering the statutory prohibitions on Members, officers, and employees of the Senate soliciting or receiving gifts from parties with business before or interests in Senate work.
Honest Leadership and Open Government Act – Pub. L. No. 110-81, 121 Stat. 735 (2007)
The Honest Leadership and Open Government Act states that the Senate Select Committee on Ethics shall “develop and revise, as necessary” regulations governing privately sponsored travel; “conduct ongoing ethics training and awareness programs”; and issue annual reports describing its activities.
Stop Trading on Congressional Knowledge Act (STOCK Act) – Pub. L. 112-05, § 17, 126 Stat. 291 (2012)
The Stop Trading on Congressional Knowledge Act (STOCK Act) states that the Senate Select Committee on Ethics shall “issue interpretive guidance of the relevant rules of [the] chamber, including rules on conflicts of interest and gifts, clarifying that a Member of Congress and an employee of Congress may not use nonpublic information derived from such person’s position as a Member of Congress or employee of Congress or gained from the performance of such person’s official responsibilities as a means for making a private profit.”
Code of Ethics for Government Service – H.R. Con. Res. 175, 85th Cong. (1958)
The Code of Ethics for Government Service sets out ten standards of conduct that should be adhered to by all government employees, including officeholders.