The formation of all ore deposits can be linked to three fundamental processes (Fig. 1): (1) mobilization of elements in one or several source regions; (2) transport of ore and non-ore constituents from a source region to the site of deposition and beyond; and (3) concentration of ore constituents, normally at the site of deposition. All three processes are interrelated, particularly in the case of hydrochemical deposits in which specific chemical mechanisms responsible for keeping metals in the ore fluid (chemical transport) also play a key role in the processes of mobilization and deposition. For example, a metal may be leached from a source rock and enter the ore solution as a metal-organic complex (in this case, metal-organic complexing is the chemical transport mechanism). It can then be transported physically by the ore fluid as a metal-organic complex, and finally, the metal can be precipitated by the breakdown of the metal-organic complex. Thus, for many hydrothermal, residual, and chemical sediment deposits, an understanding of the chemical transport mechanism is a key to understanding the related processes of mobilization and deposition. In this chapter, the focus is on the role of organic matter as a chemical transport agent in aqueous ore-forming systems (i.e., hydrothermal, residual, and chemical sediment deposits). In these systems, ore and nonore constituents are carried primarily by aqueous fluids. The transport of ore metals in ore fluids can take place as dissolved aqueous species (e.g., metal-organic complexes), or within a suspension in which metals are bound to organic particles, or within a crude oil phase (liquid petroleum). Of these possibilities, only chemical transport in solution will be considered in the following sections. First, the role of dissolved organic matter as a metal-transport agent in aqueous ore fluids will be discussed at some length. Next, our current understanding of ore-metal transport via petroleum is reviewed. Finally, the relative importance of inorganic and organic mechanisms of ore-metal transport will be briefly commented upon.