3rd parallel may refer to:

• 3rd parallel north, a circle of latitude in the Northern Hemisphere
• 3rd parallel south, a circle of latitude in the Southern Hemisphere

• Mainstream medicine
• Mainstream Publishing
• Mainstream (Quiet Sun album)
• Mainstream Records
• Mainstream river snail
• Mainstream rock
• Mainstream Rock
• Mainstream Rock Chart
• Mainstream Rock (chart)
• Mainstream Rock Tracks Chart
• Mainstream Rock Tracks chart
• Mainstream science
• Mainstream Science on Intelligence
• Mainstreams of Modern Art
• Mainstream stereotypes
• Mainstream stereotyping
• Mainstream top 40
• Mainstream Urban
• Mainstreet
• MainStreet
• Main Street(album)
• Main Street Arkansas
• Main street arkansas
• Main Street Armory
• Main Street Bank