Our main approach is to decipher the genetic basis of natural variation in quantitative traits (QTs) associated with diseases and conditions, as QTs are more amenable to analysis than the disease as a whole. We study cross-sectional cohorts of diverse populations recruited from Croatia and Scotland, in which a range of traits were collected from medical examinations, questionnaires and biochemical assays. Plasma, serum and urine have been stored from each cohort participant, allowing additional lab-based measures to be derived, and new hypotheses to be tested. Our main analysis tool, single trait, single marker genome-wide association study (GWAS), has resulted in the successful association of many common genetic variants, of relevance to a wide range of complex diseases. This work now mostly takes place within large consortia, pulling together resources nationally and internationally. Our core research continues to revolve around this approach, with numerous traits measured (including glycomics) or planned (e.g. proteomics) in thousands or tens of thousands of participants. Although the contribution of the associated genetic variants into variation of the studied trait is generally small, the findings can illuminate or highlight novel biological pathways and function.