Crowding and a lack of space in the permanent dentition are amongst the most common orthodontic problems encountered in orthodontic patients. Often the aetiology of these problems is linked to premature loss of one or more deciduous teeth with corresponding loss of space. Many of these cases could have been prevented or their severity alleviated if the practitioner employed adequate planning and space maintenance during initial treatment in the mixed dentition. A review of some of the current orthodontic space maintenance appliances and their indications is presented along with a table to aid the practitioner in treatment planning.