In situ electrochemical scanning tunneling microscopy is used to study the coarsening of platinum islands at potentials of 0.4, 0.5, and 0.6 V in the double-layer region. Several interesting surface island reconstruction processes were observed, namely, (1) growth of small polycrystalline platinum islands; (2) shape- and size-limited platinum island growth; and (3) growth of platinum islands accompanied by disappearance of nearby islands. It is evident that these potential-induced coarsening processes can be explained by Gibbs-Thomson theory as a variant of Ostwald ripening. Details of the island reconstruction processes are described, and the possible influences of these phenomena on fuel cell operation are discussed.