Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. The term metallome has been introduced by R.J.P. Williams by analogy with proteome as distribution of free metal ions in every one of cellular compartments. Subsequently, the term metallomics has been coined as the study of metallome. Szpunar (2005) defined metallomics as "comprehensive analysis of the entirety of metal and metalloid species within a cell or tissue type". Therefore, metallomics can be considered a branch of metabolomics, even though the metals are not typically considered as metabolites.