Background: The totality of evidence shows that high salt intake increases cardiovascular risk, and a number of studies have suggested its link with diabetes mellitus. Many studies also indicate that reducing salt intake will reduce these risks; however, most of the evidence is from high income countries, and little is known about how this applies to LMICs. Methods: This PhD combined systematic reviews of existing evidence and Bayesian modelling to contribute evidence on the effectiveness of salt reduction interventions, the relationship between salt intake and cardiometabolic outcomes, and factors (individual, household, national-level) affecting salt intake, with a view to better informing future interventions in LMICs. The research comprises three components: (1) a review of national salt reduction initiatives around the world; (2) an in-depth examination of evaluated salt reduction interventions at all levels of implementation in LMICs, and; (3) secondary analysis of data from LMICs using Bayesian methods. Results: The number of national salt reduction initiatives globally increased from 75 in 2014 to 96 in 2019, with a 43% and 18% increase in the number of initiatives in upper-middle- and lower-middle-income countries, respectively. Evaluations of salt reduction interventions in LMICs, implemented at all levels (i.e. not just national), showed that they were successful in producing positive outcomes such as decreased salt intake, lower sodium levels in foods, improved knowledge, attitudes and behaviours towards salt, or decreased blood pressure. The secondary analysis found limited data on cardiometabolic outcomes, apart from systolic blood pressure, and most datasets only contained individual-level factors. The Bayesian analysis showed that salt intake was positively associated with systolic blood pressure (β 0.15, 95% credible interval 0.07 to 0.22) and the factors that influenced salt intake in LMICs were sex, age, BMI, education level, history of diabetes, and salt-related attitudes. Conclusion: While there was little data on other cardiometabolic outcomes, this research reaffirms the relationship between high salt intake and blood pressure, and shows the factors that influence salt intake in LMICs. Combined with existing global evidence on the effectiveness of salt reduction interventions, the findings from this PhD produce a strong case for urgent action to reduce salt intake in LMICs.