Persulphate advanced oxidation processes (PS-AOPs) constitute an important development in the field of wastewater treatment and subsurface contamination remediation within the last two decades. Although persulphate (PS) is a very powerful oxidant, its reaction with common contaminants is relatively slow so that to achieve pollutant degradation at an acceptable rate, activation to produce reactive radicals such as sulphate and hydroxyl radicals is often necessary. Consequently, research in PS-AOPs is dominated by the search for cost-effective and sustainable activation techniques. This review provides a critical evaluation of various published techniques for the activation of PS, suggests novel explanations for important observations in the field and advances proposals to explain reaction mechanisms more consistently. Discrepancies in results and areas for further studies were identified with the view of enhancing the sustainability and reliability of PS-AOPs.