Background: Dual (using two tobacco products) and poly-tobacco product use (using more than two) account for a considerable proportion of global tobacco users. Although the global prevalence of tobacco use has declined from 33.3% in 2000 to 24.9% in 2015 and is projected to decline further in response to global tobacco control efforts, there is a growing diversity of new and alternative tobacco products in certain areas across the globe. This has contributed to the high prevalence of concurrent use of multiple tobacco products and the possibility of transitions between products, potentially increasing the health burden associated with tobacco use in areas of high prevalence of use, such as the lower-middle income countries (LMICs). Therefore, improving understanding of dual and poly-tobacco use is essential for tobacco control policy and practice. Objectives: To first systematically review existing epidemiologic evidence on current dual and poly-tobacco use among adults globally. Then, building upon the conceptual model of multiple tobacco product (MTP) use to further assess potential associations with individual and country-level factors among adults in LMICs using the latest wave of the Demographic and Health Survey (DHS). Following that, conduct an in-depth case study on Bangladesh, one of the LMICs with the highest prevalence of tobacco users globally, using the International Tobacco Control Policy Evaluation Project (ITC)-Bangladesh dataset to longitudinally investigate the patterns and factors related to transitions of different tobacco use patterns and products within different user subgroups. Lastly, to give suggestions based on the above findings to inform tobacco control regulations. Methods: A systematic review was conducted to identify studies published up to June 30, 2020, with measures of nationally representative prevalence of current dual or poly-tobacco use among adults. Next, data from 19 LMICs was obtained from the most recent wave of the DHS study, collected between 2015 and 2016, comprising 235,975 men aged 15–49 years. The prevalence was estimated using available sample weights. To estimate the associations of individual and country-level factors with tobacco use, a range of person, product, and context/situation factors were examined with multilevel models. For the longitudinal analyses, a balanced panel of 3,245 tobacco users from 2009 to 2015 in four waves of the ITC Bangladesh survey was used. Generalized Estimating Equation (GEE) models in longitudinal data analysis were utilised to evaluate predictors for transitions of cigarettes, bidis, and smokeless tobacco (SLT) use. However, only male adults were included for analyses of transitions of exclusive cigarette and exclusive bidi users, as the prevalence of both products among female adults was significantly lower in all waves of the survey. Results: Twenty studies with nationally representative prevalence data on current dual or poly-tobacco use in the adult population across 48 countries were included in the systematic review. Dual tobacco use was generally higher in Southeast Asia; poly-tobacco use was prevalent in Europe as well as in Southeast Asia. Factors associated with dual and poly-tobacco use were older age, low academic achievement, low-income status, being divorced, living in urban areas, high frequency of media use, and being a migrant. MPOWER scores were inversely associated with single tobacco use, but not with dual and poly-tobacco use. Longitudinal transition analyses revealed that age, place of residence, and psychosocial factors such as attitudes toward tobacco use and intent to quit were the most important factors associated with cigarette, bidi, and SLT use transitions in Bangladesh. Conclusions: Findings suggest that dual and poly-tobacco use are common among men, especially in LMICs in Southeast Asia. The related individual and contextual-level factors explored in this thesis could aid researchers and policy makers in identifying specific target populations, products, or consumer characteristics linked to dual/poly-tobacco use, and products transitions. This thesis highlights the need for global tobacco control regulations to be expanded and strengthened in all aspects to address all tobacco products and explicitly consider dual and poly-use to further reduce tobacco-related inequality, disease and economic burden globally.