The now-accepted mechanism was proposed by Criegee, and posits that the reaction passes through a tetrahedral intermediate before rearrangement.  
A biological version of this reaction occurs in Pseudomonas and Actinobacter bacteria; there it is catalyzed by a mono-oxygenase enzyme.  The now-accepted mechanism was proposed by Criegee, and posits that the reaction passes through a tetrahedral intermediate before rearrangement.  The discoverers of this reaction used as their reagent potassium monopersulfate; today it is generally carried out with trifluoroperacetic acid, meta-chloroperoxybenzoic acid, or a metal catalyst and hydrogen peroxide.  For asymmetric cases the more highly-substituted side preferentially migrates in order to allow for insertion of the oxygen.  Notably, it can insert an oxygen atom into a ring, turning an n-membered ring into an n+1 membered lactone.  FTP, name this reaction that oxidizes aldehydes to carboxylic acids and ketones into esters.
A biological version of this reaction occurs in Pseudomonas and Actinobacter bacteria; there it is catalyzed by a mono-oxygenase enzyme.  
Baeyer-Villiger oxidation