In military terms, 1st Regiment or 1st Infantry Regiment may refer to:

• 1st Regiment, Royal Australian Artillery
• 1st Aviation Regiment (Australia)

• 1st Marine Infantry Regiment
• 1st Infantry Regiment (France)

• Jäger Regiment 1 (Bundeswehr)
• 1st Foot Guards (German Empire)
• 1st (Emperor Alexander) Guards Grenadiers
• 1st (1st East Prussian) Grenadiers "Crown Prince"
• SS Fortress Regiment 1

• 1st Infantry Regiment (Greece)
• 1st Evzone Regiment
• 1st Raider Regiment (Greece), see 3rd Special Forces Division
• 1st Serres Regiment

• 1st Aviation Regiment (Poland)

• 1st King's Immemorial Infantry Regiment

• Durban Light Infantry, formerly 1st Infantry (Durban Light Infantry)

• 1st Infantry Regiment, King's Own Bodyguards

• 1st (Royal) Regiment of Foot
• 1st Regiment of Foot Guards
• 1st Regiment Greek Light Infantry
• 1 Regiment RLC, a unit of the Royal Logistic Corps
• 1 Regiment Army Air Corps

• 1st Infantry Regiment (United States)
• 1st Marine Regiment (United States)
• 1st Massachusetts Infantry Regiment, a unit in the American Civil War
• 1st Aviation Regiment (United States)

• 1st Fighter Regiment
• 1st Yugoslav Fighter Regiment
• 1st Transport Aviation Regiment
• 1st Training Aviation Regiment
• 1st Air Reconnaissance Regiment

• 1st Cavalry Regiment (disambiguation)
• 1st Division (disambiguation)