In chemistry, homology refers to the appearance of homologues. A homologue (also spelled as homolog) is a compound belonging to a series of compounds differing from each other by a repeating unit, such as a methylene group, a peptide residue, etc. A homolog is a special case of an analog. Examples are alkanes and compounds with alkyl sidechains of different length (the repeating unit being a methylene group -CH₂-).

Organiskaja kimija organisko savienojumu rindu, kuras locekliem ir lidziga uzbuve un lidzigas kimiskas ipašibas, bet katrs nakamais rindas loceklis atškiras no iepriekšeja par vienu —CH₂— grupu, sauc par homologu rindu, bet atseviškus šis rindas loceklus sauc par homologiem.