环烷烃，属于有机化合物，因为仅由氢（H）和碳（C）组成，故又属于烃类。又，因为其仅由单键连接，故又属于烷类。再，因为其构成如环状，故得名。环烷烃的化学通式为 C_nH_2(n+1-g)，n为碳原子数，g为环的数量。只有一环的环烷烃的命名与其同碳原子数的链状烷烃相似，如：环丙烷、环丁烷、环戊烷、环己烷等，超过20颗碳的一般被称为「环石蜡」（cycloparaffins）。

按环的大小，环烷烃可被分为小、中、大三类。环丙烷、环丁烷视作小的。常见的环戊烷、环己烷、环庚烷以及环辛烷至环十三烷是中等大小的，更大的则被视为大的环烷烃。

Cycloalkanes (also called naphthenes, but distinct from naphthalene) are types of hydrocarbon compounds that have one or more rings of carbon atoms in the chemical structure of their molecules. Alkanes are types of organic hydrocarbon compounds that have only single chemical bonds in their chemical structure. Cycloalkanes consist of only carbon (C) and hydrogen (H) atoms and are saturated because there are no multiple C–C bonds to hydrogenate (add more hydrogen to). A general chemical formula for cycloalkanes would be C_nH_2(n+1−g) where n = number of C atoms and g = number of rings in the molecule. For those cycloalkanes that have one ring in their molecules, cycloalkanes can be treated as isomers of their alkene counterparts, for example, cyclopropane and propene both have the chemical formula C₃H₆. Cycloalkanes with a single ring are named analogously to their normal alkane counterpart of the same carbon count: cyclopropane, cyclobutane, cyclopentane, cyclohexane, etc. The larger cycloalkanes, with greater than 20 carbon atoms are typically called cycloparaffins.