21 Guns or Twenty-One Guns may refer to:

• 21-gun salute, an arms salute as a military honor
• 21 Guns (band), a 1990s rock band formed by Thin Lizzy guitarist Scott Gorham
• "21 Guns" (song), a song from Green Day's 2009 album 21st Century Breakdown
• "Twenty-One Guns" (ER), a 2006 episode from the 12th season of the medical drama ER
• "Twenty-One Guns", a song on the 1996 split EP Ignite / Good Riddance

• N.N. Kilburn
• NN Kilburn
• N. N. Konstantinov
• N N Krishnadas
• NN Krishnadas
• NNL
• NNL (disambiguation)
• NNM
• N,N'-malonylurea
• NNM (disambiguation)
• N,N'-methylene bisacrylamide
• N,N'-Methylenebisacrylamide
• N,N'-Methylene bisacrylamide
• NNMF
• N N Miklukho-Maklai Institute of Ethnology and Anthropology
• NN Miklukho-Maklai Institute of Ethnology and Anthropology
• NNMREC
• NNMT
• NNN (disambiguation)
• N,N,N,N-tetramethyl-1,4-phenylendiamin
• N,N,N',N'-tetramethylnaphthalene-1,8-diamine
• N,N,N-triethylamine
• N,N,N-trimethyl-4-phosphoryloxytryptamine
• N,N,N-trimethylethenaminium hydroxide
• N,N,N-trimethylglycine