Complex commonly refers to:

• Complexity, the behaviour of a system whose components interact in multiple ways so possible interactions are difficult to describe
  • Complex system, a system composed of many components which may interact with each other
• Complex (psychology), a core pattern of emotions etc. in the personal unconscious organized around a common theme such as power or status

Complex may also refer to:

• Complex (English band), formed in 1968, and their 1971 album Complex
• Complex (band), a Japanese rock band
• Complex (album), by Montaigne, 2019, and its title track
• Complex (EP), by Rifle Sport, 1985
• "Complex" (song), by Gary Numan, 1979
• "Complex", a song by Katie Gregson-MacLeod, 2022
• "Complex" a song by Be'O and Zico, 2022
• Complex Networks, publisher of the now-only-online magazine Complex

• Protein–ligand complex, a complex of a protein bound with a ligand
• Exosome complex, a multi-protein intracellular complex
• Protein complex, a group of two or more associated polypeptide chains
• Species complex, a cluster of very similar species difficult to delimit
• Pre-Bötzinger complex, a cluster of interneurons in the ventral respiratory group of the medulla of the brainstem

• Coordination complex, a central atom or ion and a surrounding array of bound molecules or ions
• Chelate complex, a coordination complex with more than one bond

• Complex number, an extension of real numbers obtained by adjoining imaginary numbers
• Complex, an element of a field of sets
• Chain complex, an algebraic structure
• Simplicial complex, a kind of topological space
• CW complex, a kind of topological space
• Line complex, a 3-dimensional family of lines in space

• Complex (geology), a unit of rocks composed of rocks of two or three types
• Complex crater, a type of large impact crater morphology
• Volcanic complex, a group of volcanoes
• Complex volcano, a volcano of mixed form
• Accretionary complex, a fossil accretionary wedge

• Building complex, a group of inter-related buildings
  • Housing complex, specifically residential
  • Market complex, group of stores or business firms in a marketplace having common walkway(s), usually enclosed within a boundary or situated under one roof
• UCL Centre for Mathematics and Physics in the Life Sciences and Experimental Biology (CoMPLEX), part of UCL Faculty of Mathematical and Physical Sciences, London, UK

• All pages with titles beginning with Complex
• All pages with titles containing Complex
• Complexity (disambiguation)
• Complexity theory (disambiguation)
• Military–industrial complex