Occasional (non-daily) smokers pose difficulties for classic withdrawal-based addiction theory because they can regularly go without cigarettes for days with no apparent discomfort. Occasional smokers can be further divided into two subgroups: (1) occasional smokers who used to smoke daily, also known as former-daily occasional smokers (FDO) and (2) occasional smokers who never smoked daily (NDO). Little is known about the situations under which occasional smokers typically smoke their cigarettes, and even less is known about how daily smokers transition to occasional smoking. Three exploratory studies were conducted to examine the following questions. (1) What proportions of smokers are occasional and daily smokers, and how have the respective proportions changed as social norms become increasingly anti-smoking and as smoking continues to decline? (2) When are occasional smokers most likely to smoke, and how do they compare with daily smokers? (3) How do daily smokers transition to smoking occasionally? When they first cut back to smoking only about half the days in a month, which days are they most likely to forgo? The first study analyzed data from the 1996, 1999, 2002, and 2005 California Tobacco Surveys (CTS); the second used data from the 2002 CTS Young Adult Supplement, which includes questions on smoking situations; and the third focused on 152 occasional smokers recruited from the Internet for detailed interviews on smoking situations. The studies found that occasional smokers represent substantial proportions of all current smokers. Moreover, as the overall smoking prevalence declined from 17.7% in 1996 to 14.2% in 2005, the proportions of occasional smokers did not decrease, as would be predicted by their significantly higher cessation rates compared to that of daily smokers. The proportion of FDO smokers increased, though not significantly, from 1996 to 2005: 12.3% to 14.2% for men and 12.9% to 16.8% for women. The NDO proportion increased from 11.9% to 15.3% for men and decreased slightly from 10.6% to 9.5% for women; but again neither change is statistically significant. The pattern of smoking situations for FDO smokers was quite similar to that of NDO smokers, with greater overall likelihood of smoking in social or episodic situations (i.e., socializing with friends or going out) rather than solitary or routine situations (i.e., working or driving). Both differed significantly from that of daily smokers who tended to smoke across a variety of situations. Most FDO smokers (64.3%) had converted to occasional smoking through quitting smoking completely and then returning to smoking non-daily, rather than by cutting down their consumption gradually. Based on these findings we propose a model explaining how daily smokers could transition to occasional smoking. The minority of daily smokers who cut down gradually to non-daily smoking first forgo those days involving routine, solitary situations, such as at home with no other smokers present. The majority who quit daily smoking and later relapse to occasional smoking restrict their smoking mostly to days that involve episodic social situations, such as at parties. In either case, the results from the present three studies show that FDO smokers are virtually indistinguishable from NDO smokers in their current smoking situations, suggesting their previous smoking pattern has very limited influence on their current smoking behavior.