Determining early-life risk factors for obesity in later life is essential in order to effectively target preventative interventions to reduce obesity. The aim of this systematic review was to investigate current evidence to determine whether the timing of introducing solid foods is associated with obesity in infancy and childhood. Relevant randomized and observational studies from developed countries were identified by searching the following six bio-medical databases (Medline, Embase, British Nursing Index, CINAHL, Maternity and Infant Care, and PsycINFO) and hand-searching reference lists. Studies of pre-term or low birthweight infants were excluded. Twenty-four studies met the inclusion criteria for the systematic review. Data from over 34,000 participants were available for interpretative analysis. No clear association between the age of introduction of solid foods and obesity was found. It is likely that a whole family approach to obesity prevention will be most effective and health professionals should continue to promote healthy infant feeding in line with national recommendations.