Childhood asthma is a common condition where symptoms are often present from preschool years and continue into adult life for many individuals. Asthma can be treated but not cured and the most promising means to reduce asthma prevalence is prevention. This talk will address two key questions relevant to asthma prevention: “what are the early influences on asthma?” and “when are they acting?”. The focus will be on the fetal and preschool years and will include interactions between genetic and environmental factors. The audience will gain an understanding of the complexity of the early origins of asthma and also take home some (hopefully useful) practical advice for parents and governments.