The Wacker process or the Hoechst-Wacker process refers to the oxidation of ethylene to acetaldehyde in the presence of a palladium(II) chloride catalyst.
It was originally developed in 1956 by the German chemical firm Wacker Chemie, and is still widely in use for the industrial production of acetaldehyde, which is used to make acetic acid, synthetic resins, rubbers and many other chemical products.
The mechanism of the reaction has been widely investigated for 70+ years, and has still not been fully explained.
Further reading Wikipedia