The M21 highway () was a road in Moldova, which linked ChiÃÂinÃÂu to the border with Ukraine near DubÃÂu via DubÃÂsari. It was long, and formed part of the European route E584 of the International E-road network. Furthermore, it also shared a small segment with the E58 and E581 north-west of ChiÃÂinÃÂu.
In 2016, a government decision decommissioned the M21 and integrated the entirety of the route into the M1 highway.
The M21 highway began at an intersection with the R1 road west of the capital city of ChiÃÂinÃÂu. Heading north-east, it then met with the M2, M14 (now dubbed "M5") and R4. This was the northern terminus of the M21's interference with the E58 and E581 and the southern terminus of the interference with the European route E584.
Between ChiÃÂinÃÂu and DubÃÂsari, the road doubled the republican road R4, which has its eastern terminus near Criuleni. The road then crossed the Dniester to reach the unrecognized state of Transnistria.
Immediately after entering the Transnistrian territory, the road reached a roundabout with the M4 highway, which provides access to DubÃÂsari, which the M21 bypassed in the south-east. The road then continued to head north-east to the border with Ukraine near DubÃÂu, from where it continues as the Ukrainian highway M13, towards Kropyvnytskyi.