The aim of this thesis was to summarise and evaluate the methods of slow maxillary expansion and rapid maxillary expansion treatments on the maxilla. It is the purpose of this study to analyse how both slow and rapid maxillary expansion treatments are used to treat transverse maxillary discrepancies by current evidences of “meta-analyses”, “systemic reviews”, any “significant randomised controlled trials”. Within these articles it was found that both SME and RME were effective but it was dependent on the age of the patient. The patient has to be in their prepubertal peak for these SME and RME treatment options to be viable.