Dairy cattle exhibit consistent variation in behaviour between individuals, referred to as temperament. In humans consistent variation in behaviour is referred to as personality and has significant associations with health and wellbeing. The studies reported in this thesis investigated whether temperament is also associated with health and welfare outcomes in dairy cattle. No universal framework for expressing temperament currently exists in cattle and temperament has previously been evaluated using both behavioural and physiological measurements. In this thesis a framework for expressing temperament, comprised of the five traits Activity, Aggression, Boldness, Exploration and Sociability, was validated in lactating dairy cattle using factor analysis on the results of behavioural testing. The validated framework was used to quantify the temperaments of cattle at 21, 60 and 100 days lactation. Measurements of physiological parameters, hair cortisol concentration, saliva cortisol concentration, heart rate variability and maximum eye temperature, were taken alongside behavioural testing to determine whether they were reliable indicators of temperament. Temperament testing was consistent between 21 and 100 days lactation but not between 21 and 60 days or 60 and 100 days, possibly due to the effect of milk yield on the autonomic nervous system. Cortisol concentrations and eye temperature had no consistent relationship with single temperament traits but heart rate and sympathetic response, quantified by heart rate variability, were reliable indicators of Boldness during a startle test at both 21 and 100 days lactation. The validated framework was used to test a cohort of dairy calves pre-weaning, post-weaning, pre-puberty and post-puberty to determine whether temperament of cattle is consistent during maturation. This study found that behavioural measures of temperament were not consistent between measurements but parasympathetic activity in a crush test and eye temperature response to a novel arena, startle and novel object test were consistent from pre-weaning to post-puberty. The temperament scores and eye temperature measurements were used to quantify associations between temperament and risk of infectious disease. High Activity calves were significantly more likely to be treated for pneumonia and high Activity cows at 21 days lactation were significantly more likely to be treated for an infection from 21-100 days lactation. This work demonstrated that temperament can be measured consistently and is associated with greater risk of infectious diseases in both lactating cattle and youngstock.