E-cigarettes (ECs) and heated tobacco products (HTPs) have become popular in Korea; hence, it is important to determine whether ECs and HTPs are less hazardous than combustible cigarettes (CCs). In general, the levels of harmful and potentially harmful constituents (HPHCs) are lower in ECs and HTPs than in CCs, although the levels of some heavy metals and HPHCs are higher in ECs and HTPs than in CCs. ECs and HTPs showed possible adverse effects on respiratory and cardiovascular system function, which could result in chronic respiratory and cardiovascular system diseases in animals. An analysis of biomarkers showed that ECs had possible adverse health effects on the respiratory and cardiovascular systems, in addition the effects of HTP on respiratory and cardiovascular systems were not significantly different than those of CC. Epidemiological studies identified positive associations between EC use and asthma, chronic obstructive pulmonary disease, and myocardial infarction. Only one epidemiologic study reported a positive association between ever using HTPs and asthma, allergic rhinitis, and atopic dermatitis among adolescents. Modelling studies of ECs did not show consistent findings regarding the health effects compared with those of CCs. A modeling study of HTPs, performed by tobacco industry, has been criticized for many unfounded assumptions. Lower levels of HPHCs in ECs and HTPs, compared with those in CCs, cannot be directly translated into health benefits because the relationship between exposure and effects is non-linear for cardiovascular diseases and because the duration of exposure is more important than the level of exposure in determining lung cancer mortality. In summary, there is no definite health benefit in using ECs or HTPs instead of CCs, for the individual or the population; hence, tobacco control measures should be the same for ECs, HTPs, and CCs. ECs and HTPs have become popular in Korea; hence, it is important to determine whether ECs and HTPs are less hazardous than CCs.