Md. Code, Public Safety § 13-202

(a) Except as provided in subsection (b) of this section, the militia consists of able–bodied individuals who are:

(1) citizens of the State;

(2) citizens of the United States who take an oath of allegiance to the State; or

(3) of foreign birth and who:

(i) are residents of the State; and

(ii) have declared their intention to become citizens of the State.

(b) Subject to subsection (c) of this section, an individual is exempt from subsection (a) of this section if the individual:

(1) is exempted by the laws of the United States;

(2) is exempted by the laws of the State;

(3) is a member of a regularly organized fire or police department in a county, city, village, or town;

(4) is a judge or clerk of a court of record;

(5) is a register of wills and deeds;

(6) is a sheriff;

(7) is a member of the clergy;

(8) is a practicing physician;

(9) is a superintendent, officer, or assistant of a hospital or correctional facility;

(10) has been judged mentally incompetent;

(11) is addicted to narcotic drugs; or

(12) has been convicted of an infamous crime.

(c) An individual exempted under subsection (b)(3) through (12) of this section shall be available for military duty in case of war, insurrection, or invasion, or when the danger of war, insurrection, or invasion is imminent.