Ion mobility spectrometry (IMS), using standalone instrumentation and hyphenated with mass spectrometry (IM-MS), has recently undergone significant expansion in the numbers of users and applications, particularly in sectors outside its established user base; predominantly military and security applications. Although several IMS reference standards have been proposed, there are no currently universally recognised reference standards for the calibration and evaluation of mobility spectrometers. This review describes current practices and the literature on chemical standards for validating IMS systems in positive and negative ion modes. The key qualities and requirements an 'ideal' reference standard must possess are defined, together with the instrumental and environmental factors such as temperature, electric field, humidity and drift gas composition that may need to be considered. Important challenges that have yet to be resolved are also identified and proposals for future development presented.