A writing instrument comprising: a main body having a first end, a second end and a longitudinal axis extending in a longitudinal direction through the first and second ends; a writing tip disposed at the first end of the main body; an ink-containing cartridge; a rear body comprising an elongate housing having a first end a second end and an access opening at the first end allowing the ink-containing cartridge to be inserted into or removed from the housing, the housing extending in a loading direction between the first and second ends of the elongate housing; and an articulation means connecting the main body and the rear body. The articulation means allows the rear body to pivot with respect to the main body about an axis of articulation perpendicular to the longitudinal axis, between a loading or open position in which the access opening is rotated away from the longitudinal axis of the main body and a closed position in which the longitudinal direction and the loading direction substantially coincide.