N.H. REV. STAT. ANN. 53-A:2 Public Agency Defined.
For the purposes of this chapter, the term “public agency” shall mean any political subdivision of this state or of any adjoining state and any quasi-municipal corporation, including but not limited to school districts, village districts, regional water districts, and special districts.
N.H. REV. STAT. ANN. §53-A:3 Joint Exercise of Powers. –Any power or powers, privileges or authority exercised or capable of exercise by a public agency of this state may be exercised jointly with any other public agency of this state. Such authority shall include, but not be limited to, the power to enter into agreements to share tax revenues resulting from local economic development efforts and with respect to cities and towns, the power to form the entities and conduct the activities provided for in RSA 162-G.
I. Any 2 or more public agencies may enter into agreements with one another for joint or cooperative action pursuant to this chapter. Appropriate action by ordinance, resolution or other action pursuant to law of the governing bodies of the participating public agencies shall be necessary before any such agreement may enter into force.
Link to the full statute can be found here: http://www.gencourt.state.nh.us/rsa/html/III/53-A/53-A-3.htm