Complex commonly refers to:

Complexity, the behaviour of a system whose components interact in multiple ways so possible interactions are difficult to describeComplex system, a system composed of many components which may interact with each otherComplex (psychology), a core pattern of emotions etc. in the personal unconscious organized around a common theme such as power or statusComplex may also refer to:

== Arts, entertainment and media ==Complex (English band), formed in 1968, and their 1971 album ComplexComplex (band), a Japanese rock bandComplex (album), by Montaigne, 2019, and its title trackComplex (EP), by Rifle Sport, 1985"Complex" (song), by Gary Numan, 1979Complex Networks, publisher of magazine Complex, now online

== Biology ==Protein–ligand complex, a complex of a protein bound with a ligandExosome complex, a multi-protein intracellular complexProtein complex, a group of two or more associated polypeptide chainsSpecies complex, a cluster of very similar species difficult to delimitPre-Bötzinger complex, a cluster of interneurons in the ventral respiratory group of the medulla of the brainstem

== Chemistry ==Coordination complex, a central atom or ion and a surrounding array of bound molecules or ionsChelate complex, a coordination complex with more than one bond

== Mathematics ==Complex number, an extension of real numbers obtained by adjoining imaginary numbersComplex polytope, a generalization of a polytope in a complex Hilbert spaceComplex analysis, the study of functions of complex numbersComplex, an element of a field of setsChain complex, an algebraic structureSimplicial complex, a kind of topological spaceCW complex, a kind of topological spaceLine complex, a 3-dimensional family of lines in space

== Geology ==Complex (geology), a unit of rocks composed of rocks of two or three typesComplex crater, a type of large impact crater morphologyVolcanic complex, a group of volcanoesComplex volcano, a volcano of mixed formAccretionary complex, a fossil accretionary wedge

== Other uses ==Building complex, a group of inter-related buildingsHousing complex, specifically residentialUCL Centre for Mathematics and Physics in the Life Sciences and Experimental Biology (CoMPLEX), part of UCL Faculty of Mathematical and Physical Sciences, London, UK

== See also ==All pages with titles beginning with ComplexAll pages with titles containing ComplexComplexity (disambiguation)Complexity theory (disambiguation)Military–industrial complex