FAR 61.51:
(e) Logging pilot-in-command flight time. (1) A recreational, private, or commercial pilot may log pilot-in- command time only for that flight time during which that person—
(i) Is the sole manipulator of the controls of an aircraft for which the pilot is rated;
(ii) Is the sole occupant of the aircraft; or
(iii) Except for a recreational pilot, is acting as pilot in command of an aircraft on which more than one pilot is required under the type certification of the aircraft or the regulations under which the flight is conducted.
(2) An airline transport pilot may log as pilot-in-command time all of the flight time while acting as pilot-in-command of an operation requiring an airline transport pilot certificate.
(3) An authorized instructor may log as pilot-in-command time all flight time while acting as an authorized instructor.
from FAR 135.243
(c) Except as provided in paragraph (a) of this section, no certificate holder may use a person, nor may any person serve, as pilot in command of an aircraft under IFR unless that person—
(1) Holds at least a commercial pilot certificate with appropriate category and class ratings and, if required, an appropriate type rating for that aircraft; and
(2) Has had at least 1,200 hours of flight time as a pilot, including 500 hours of cross country flight time, 100 hours of night flight time, and 75 hours of actual or simulated instrument time at least 50 hours of which were in actual flight; and
(3) For an airplane, holds an instrument rating or an airline transport pilot certificate with an airplane category rating; or
(4) For a helicopter, holds a helicopter instrument rating, or an airline transport pilot certificate with a category and class rating for that aircraft, not limited to VFR.
I hate it that you guys made me quote the FARs. I swear I'll hire you anyway.