Background To better understand the process of quitting from the ex-smokers' perspective, and to explore the role spontaneity and planning play in quitting. Methods Qualitative grounded theory study using in-depth interviews with 37 Australian adult ex-smokers (24-68 years; 15 males, 22 females) who quit smoking in the past 6-24 months (26 quit unassisted; 11 used assistance). Results Based on participants' accounts of quitting, we propose a typology of quitting experiences: measured, opportunistic, unexpected and naïve. Two key features integral to participants' accounts of their quitting experiences were used as the basis of the typology: (1) the apparent onset of quitting (gradual through to sudden); and (2) the degree to which the smoker appeared to have prepared for quitting (no evidence through to clear evidence of preparation). The resulting 2 x 2 matrix of quitting experiences took into consideration three additional characteristics: (1) the presence or absence of a clearly identifiable trigger; (2) the amount of effort (cognitive and practical) involved in quitting; and (3) the type of cognitive process that characterised the quitting experience (reflective; impulsive; reflective and impulsive). Conclusions Quitting typically included elements of spontaneity (impulsive behaviour) and preparation (reflective behaviour), and, importantly, the investment of time and cognitive effort by participants prior to quitting. Remarkably few participants quit completely out-of-the-blue with little or no preparation. Findings are discussed in relation to stages-of-change theory, catastrophe theory, and dual process theories, focusing on how dual process theories may provide a way of conceptualising how quitting can include elements of both spontaneity and preparation.