Clandestine is an adjective meaning that its reference is something secret or guerrilla in nature, such as certain activities executed by spies.

• Clandestine operations, secret or covert operations
• National Clandestine Service, formerly the CIAs Directorate of Operations
• Clandestine chemistry is chemistry carried out in secret.
• Clandestinity is an impediment to marriage in the canon law of the Roman Catholic Church.
• Clandestine is a clothing line by Peter Wentz of Fall Out Boy.
• Clandestine is a novel by James Ellroy.
• Clandestine is an album by Entombed.
• Clandestine is a MUD.
• Clandestine is a short film by AFI (band).
• Clandestine was a Celtic music band from Houston, Texas.
• ClanDestine is a comic book series by Alan Davis and published by Marvel Comics about a family of British superheroes in the Marvel Universe.
• Clandestino is an album by Manu Chao.
• Clandestiny is an adventure game.
• CIRCA (Clandestine Insurgent Rebel Clown Army) is an antimilitarist British action group of clowns dressed in army uniforms.