Iteroselectivity is defined as the preferential formation of products (i.e. iteromers) differing by the number of repeating chemical transformations the starting substrate underwent, where preferential means different from a normal product distribution (see below). The products of an iterative reaction are not isomers and thus must be named iteromers instead of iteroisomers. Repeating chemical transformations designate reactions occurring on equivalent starting functional groups yielding equivalent final functional groups (e.g. alkylation of primary alcohols under the same conditions affording ethers). We originally proposed the name "iteroselectivity" as this type of selectivity concerns iterative processes such as the modification of a given number of functional groups iteratively. The iteroselectivity discussed herein applies only to one-pot reactions involving iterative chemical steps and should not be confused with sequential multi-step processes such as peptide syntheses relying on protection/deprotection steps. Iteroselectivity may originate from a wide diversity of phenomena such as electronic, steric, supramolecular effects, or even difference in solubilities. Iteroselectivity under kinetic control involves a modification of the reactivity after a given number of iterations, i.e. activating or deactivating one iteromer in regard to other iterations of the chemical reaction, thus accumulating an iteromer regardless of its relative stability compared to other iteromers. Thermodynamic control is only seen at equilibrium in reversible reactions in which the most stable iteromer(s) will form preferentially.