Mechanical size reduction methods have dominated the scene in nearly all industries involved with comminution since their beginning. However, the various challenges and limitations of mechanical methods have maintained widely open the opportunities for non-mechanical milling methods. This review analyzes critically several different approaches, including thermal shock, microwaves, lasers, pressure variation, high voltage pulses and ultrasound. While interest in some of them, namely thermal shock and pressure variation, has nearly vanished, others are intensively studied at present and seem to be on the brink of becoming industrially-available technologies. Examples of the later are microwaves and high voltage pulses. The large variety of materials and applications that involve size reduction and the nearly universal reliance on mechanical methods suggests that non-mechanical methods have found niche applications and that type of application with continue to grow. Examples of these are lithotripsy and laser ablation, which already find applications in narrow, but important fields.