Excess sugar consumption has been associated with adverse health outcomes and recommendations have been made globally to reduce intake of free sugars across all ages. Despite this, sugar consumption in England remains high and in 2016 government introduced a voluntary reformulation policy aiming to reduce the sugar content of certain products. The aim of this DrPH thesis was to examine the potential role of voluntary reformulation policy in reducing population consumption of sugar, and I examined this using three discrete studies. I conducted a systematic review of empirical evidence examining the impacts of sugar reformulation policy. I identified five studies of voluntary policies, three of which focused on England’s policy. Studies showed small reductions in the sugar content of products overall and the volume of sugar purchased (or sold), however the certainty of evidence was assessed as very low. Greater reductions were reported for certain product categories, although most sugar reduction targets had not been met and reductions were still modest. No studies had examined the effects of reformulation policy on sugar consumption. I conducted a qualitative case study of England’s voluntary salt reformulation policy, using existing evidence to examine implementation factors relevant to policy effectiveness. Evidence suggested that population salt intake was reduced when the policy was implemented alongside food labelling and consumer awareness policies, with clear reformulation targets, and monitoring of progress using soft regulation. Gradual reduction of salt in products was considered technically feasible and acceptable to consumers. Leadership external to (yet backed by) government, resourcing for policy implementation, transparency in implementation and governance were also important. I conducted a quantitative study using Kantar FMCG consumer panel data to explore changes in sugar content, portion sizes and purchases of breakfast cereals, sweet and chocolate confectionary between 2015 and 2018. I saw evidence of a reduction in the sugar content of breakfast cereal products only. Changes in sugar content of products were due to a combination of reformulation and product renewal. There was no evidence of reductions in portion sizes of single serve products or in the total volume of sugar purchased. Limited evidence suggests that voluntary sugar reformulation policy might lead to modest reductions in the sugar content of certain products and the volume of sugar purchased, although the potential impact of reductions on population sugar consumption is unknown. The lack of any comprehensive, independent evaluation of England’s sugar reformulation policy is a missed opportunity to generate new empirical evidence based on policy implementation. Application of the regulatory approaches used by the Food Standards Agency during the initial phase of England’s salt reformulation policy should be considered to enhance the potential impacts of voluntary reformulation policy for sugar. Voluntary reformulation policy will have the greatest impact when implemented alongside other policies focused on reformulation.