Abstract: A writing instrument includes a barrel defining a channel, an arcuate cam member coupled to the barrel and a writing element in communication with the cam member. The cam member is rotatable between a first position in which a writing end of the writing element is retracted within the channel and a second position in which the writing end of the writing element is extended out of the channel. The cam member rotates about an axis of rotation that is transverse to the longitudinal axis of the writing instrument. Various features which improve the functioning of the writing instrument or cam member may be provided separately or in combination.