M21 is a Ukrainian international highway (M-highway) which connects Zhytomyr and Vinnytsia to the border with Moldova.

[1] The highway also connects two major transnational corridors, Pan-European Corridor IX and the transportation corridor "Europe-Asia".

The entire route is part of European route E583.

[2] The section from Zhytomyr to the Belarusian border was previously P28.

This Ukrainian road or road transport-related article is a stub.