The Julia-Kocienski reaction has become indispensable in the synthetic organic chemist's olefination toolbox. Although the stereochemical outcome of the transformation is sometimes difficult to predict, some trends can be explained by an array of mechanistic hypotheses which have been put forward since the initial disclosure of the reaction. Moreover, several important developments have been recently reported and are summarised in this microreview. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)