O-Type may refer to:

• O-type asteroid
• O type blood
• O-type star
  • O-type giant
  • O-type main sequence star
  • Subdwarf O star

• Tallmadge High School
• Tallmadge, Michigan
• Tallmadge (OH)
• Tallmadge Township, Summit County, Ohio
• Tall Man
• Tall Man (album)
• Tallman East Airport
• Tallmansville, West Virginia
• Tallmansville, WV
• Tallmantz Phoenix P-1
• Tall meadow oat
• Tall Melilot
• Tall Morning Glory
• Tallness
• Tall oat-grass
• Tall oatgrass
• Tall oil
• Tall Oil
• Talloires Declaration
• Talloires, France
• Tallong Public School
• Tallong railway station
• Tallowa Dam
• Tallow Chandlers Company
• Tallow, County Waterford