M5 may refer to:

• The M5 motorway in England, running from Birmingham to Exeter
• Messier object 5, a star cluster in the constellation of Serpens
• M5, the homicidal computer featured in the Original Star Trek episode "The Ultimate Computer"
• The BMW M5, a high-performance version of the BMW 5 Series automobile manufactured by BMW.
• M5 fiber is a high-strength polymer developed by Magellan Systems International.
• M5 Industries , a visual effects company founded by Jamie Hyneman, co-host of MythBusters