Palladium-catalysed cross-coupling reactions are routinely used in the synthesis of important organic and organometaltic compounds, including advanced materials and natural products. Industry and academia depend heavily on these ubiquitous transformations. Their success is quite remarkable, but not without their share of problematic and sometimes unusual observations, which continue to probe our fundamental understanding of these reactions. Through an identification of side-reactions, our train of thought of a well-known reaction can be challenged. In this review we identify exemplary processes and show how they have been exploited in synthetic chemistry. A deeper insight into well-established processes is provided, which alerts us to new synthetic transformations. On one hand, it is of significant interest to understand how to minimise unwanted reactions and their side-products, but on the other, one can seek to exploit such reaction pathways and develop new synthetic methodologies. Either way, synthetic chemists only stand to benefit from such findings, which, more often than not, stimulate further research into this ever-expanding field. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)