Greece Interstate 3 is a highway that is the old national road from Eleusis to Larissa, and near Tyrnavos to Elassonas and the new national road up to the FYROM border near Niki. It is also E65 north of Larissa. In the 1980s, the highway opened bypass of Tyrnavos and Elassonas. It is one of the longest higways in Greece. It is bypassed by Greece Interstate 1 since the 1960s up to Larissa. It used to serve as a highway to Thessaloniki with the same route up to Larissa.

There had been some farmer's protests against low prices as they spilled milk on this highway in 2003. It lasted for a couple of days and tractors blocked the entire highway.

The highway passes and by-passes through these places:

• Eleusis (western part)
• Mandra
• Thiva
• Levadeia
• Lamia, and bypasses
• Pharsalus/Farsala
• Larissa
• Tyrnavos, and bypasses
• Elassonas, and bypasses
• Kozani, and bypasses
• Ptolemaida, and bypasses
• Florina
• Niki