It may at first sight seem strange that concepts developed by Albert Einstein in the first decade of the 20th century to explain the structure and dynamics of the cosmos should have any relevance to chemistry. However, it is now quite clear that the chemical behaviour of the heavier elements in particular is dominated by what are termed “relativistic effects”. This article explores the implications of this for the coordination and chemisorption of carbon monoxide and unsaturated hydrocarbons, and their reactions in homogeneous and heterogeneous catalysis involving the platinum group metals.