The APG III system (Angiosperm Phylogeny Group III system) of flowering plant classification is the third version of a modern, mostly molecular-based, system of plant taxonomy. The system was published in 2009 by the Angiosperm Phylogeny Group, 6½ years after its predecessor the APG II system was published, and 11 years after the initial APG system was published in 1998.

The APG III system (Angiosperm Phylogeny Group III system) of flowering plant classification is the third version of a modern, mostly molecular-based, system of plant taxonomy. The system was published in 2009 by the Angiosperm Phylogeny Group, 6½ years after its predecessor the APG II system was published, and 11 years after the initial APG system was published in 1998.