Child growth failure (CGF) is associated with high morbidity which can predispose children to impaired cognitive development. Despite decades of interventions, a high level of CGF has persisted in Ethiopia. A likely key reason for this situation is the undetermined role of water, sanitation, and hygiene (WASH) on child growth. The overarching aim of this thesis was to examine the effects of WASH on child growth in Ethiopia. Data were extensively analysed from the Ethiopia Demographic and Health Survey (EDHS) from 2000 to 2016, and a systematic review was conducted for the thesis. Logistic regression models were fitted to assess the association of access to household WASH facilities with child growth outcomes. We conducted a systematic review and meta-analysis of WASH interventions, separately, and when combined with nutrition. To estimate trends of CGF, we used adjusted margins of predicted probabilities. Socioeconomic inequalities in CGF were estimated using a concentration curve and indices. Children with access to improved household WASH facilities were 33% less likely to have stunting. Non-randomized controlled trial studies (non-RCTs) showed an effect of WASH interventions alone on height-for-age (HAZ) (Mean difference (MD)= 0.14; 95% CI: 0.08 to 0.21) while RCTs did not. WASH alone of non-RCTs and RCTs that were delivered over 18 to 60 months indicated an effect on HAZ (MD = 0.04; 95% CI: 0.01 to 0.08). RCTs showed an effect on children < 2 years (MD = 0.07; 95% CI: 0.01 to 0.13). WASH combined with nutrition showed an effect on HAZ compared with no intervention (MD = 0.13; 95% CI: 0.08 to 0.17) and on weight-for-age (WAZ) (MD = 0.09; 95% CI: 0.05 to 0.13). There was evidence of a decline in levels of CGF between 2000 and 2016 in Ethiopia. In particular, there was a greater steady decline between 2005 and 2011 compared with other periods. Access to improved household WASH facilities mainly contributed to the reduction of CGF. Between 2000 and 2016, the concentration index increased from -0.072 to -0.139 for stunting, -0.088 to -0.131 for underweight and -0.015 to -0.050 for wasting. Key socioeconomic predictors of these inequalities were identified through decomposition analyses. Socioeconomic status of the household, geographic region, antenatal care (ANC), parental education and access to household WASH facilities largely contributed to the inequalities. Access to improved household WASH facilities was strongly associated with reduced odds of stunting. WASH interventions alone improved HAZ when delivered over 18 to 60 months and in the first 1000 days of a child’s life. The effect was stronger when WASH was combined with nutrition interventions. Integrated WASH with nutrition interventions may be an effective way of improving child growth outcomes. Improving identified predictors of socioeconomic status would most likely reduce inequalities in CGF.