Several hypotheses exist on the sources and decay rates of iron-binding organic ligands. Ligand concentrations vary between ~0.2 to ~10 nM and sources and sinks are thought to be active production by iron-stressed cells, release from organic debris, photochemistry and bacterial degradation. As the concentration of ligands influences the solubility of iron, it matters for the description of iron cycling in ocean biogeochemical models how ligands are treated in them. Here we review approaches to organic complexation in present biogeochemical models and present a new dynamic model. This model for ligands is based on the concept that ligands are produced both from organic matter remineralization and phytoplankton processes, and that they are lost through bacterial and photochemical degradation, as well aggregation and to some extent in the process of phytoplankton uptake of ligand-bound iron. We discuss some results on the large-scale distribution of models, compare them to available observations, and show how the introduction of prognostic ligands affects the representation of the iron cycling in models. We also discuss some limitations of our present approach and possible future steps.