Antimicrobial resistance (AMR) in infectious disease is a major global health issue. AMR is a particular problem in low to middle-income countries (LMICs), where infectious diseases, such as diarrhoea, remain common and are commonly treated haphazardly with antimicrobials. The aim of my thesis was to provide a comprehensive study of diarrhoeal disease in children under the age of five years in the community in Ho Chi Minh City (HCMC), Viet Nam. Additionally, I aimed to fill in a knowledge gap regarding antimicrobial usage for diarrhoea, the extent of AMR organisms in healthy children within the population, and investigate a potential solution for limiting AMR in the community. Active surveillance for diarrhoea in a prospective longitudinal cohort of 748 children followed for 24 months found a high incidence of diarrhoeal disease in the urban community (71.87/100 child-years of observation [95%CI: 65.68 -78.44]). Faecal samples were screened using conventional microbiology and multiplex molecular methods and found that the aetiology of this disease is highly variable. Pathogenic bacteria and viruses were detected at a high prevalence, but the most common were Salmonella and norovirus, respectively. Antimicrobials were commonly used for diarrhoeal treatment in hospital. Additionally, a mixed-methods approach in the community found an ease of access to antimicrobials for diarrhoeal management in the community through local pharmacies. However, despite antimicrobials being widely available in the community, antimicrobial usage was almost 10 times greater in the hospitals. Widespread antimicrobial access may induce the selection of antimicrobial resistant organisms (AROs) and antimicrobial resistance genes (ARGs). An assessment of the prevalence of and risk factors for carrying AROs and ARGs demonstrated a high prevalence of carriage antimicrobial resistant Escherichia coli (E. coli) and associated resistance genes to fluoroquinolones and third generation cephalosporins. Both these groups are commonly used to treat diarrhoea in this setting. Children of higher body weight and height z-score were more likely to carry fluoroquinolones resistance genes and younger children were more likely to carry either third generation cephalosporin resistance genes individually or in combination with fluoroquinolones resistance genes. Lastly, hypothesising that improved breastfeeding practices may reduce diarrhoeal disease and impact antimicrobial usage and consequently AMR, I investigated risk factors for suboptimal breastfeeding using data from a birth cohort conducted in both an urban and a semi-rural area. The study indicated that having a Caesarean section and neonatal complications prevented mothers from breastfeeding their infants during the hospital stay. Work from this thesis will contribute to the efforts of tackling AMR in a LMIC, specifically in Viet Nam where there is extensive exposure to antimicrobials and sustained exposure to enteric pathogens.