Smoking behaviour has been suggested as a key pathway that may mediate social differences in health. Smoking behaviour is typically measured by self-report data collected at a single time point with smoking histories relying on retrospective questions on age of smoking initiation, smoking cessation and amount smoked. Our data will allow us to examine a precise smoking history, for example low level smoking and length of time since quitting (Bernaards et al., 2001) by combining self report data collected annually over long time periods. Recently it has been found that DNA methylation is a sensitive biomarker of smoking history (Philibert et al., 2013; Richmond et al., 2014). To date, more than 15 independent signals have been described associated with smoking, with evidence of life long exposure including in utero (Richmond et al., 2014), reversibility associated with smoking cessation (Richmond et al., 2014, Tsaprouni et al., 2014) in markers which may be related to inflammatory markers and blood pressure (Tsaprouni et al., 2014). Our study will represent one of the largest and most detailed to date as it will use data from 10 years of smoking history. Genome-wide epigenetic profiling using the new Illumina Infinium methylationEpic BeadChip platform will be described in 1100 individuals of European ancestry from the BHPS subsample of Understanding Society using the new Illumina Infinium MethylationEpic BeadChip which replaced the Illumina Infinium HumanMethylation450k BeadChip in Jan 2016. The new array assays 850,000 CpG sites genome-wide, and covers 90% of the sites explored in the Illumina Infinium HumanMethylation450k BeadChip. This will be able to determine new signal for smoking and examine the utility of epigenetic markers as biomarkers of smoking, in particular to examine the association of low level smoking with social and economic position independently of self-reported behaviour.