This chapter deals with morphological variation in synchronic terms. Variation is treated as a phenomenon triggered by principally language-internal causes, although it may often result from the interference of language external factors, such as contact with another language. Arguments are drawn from derivation, compounding, and inflection, and components such as reduction of allomorphy, paradigmatic leveling, selectional properties, headedness, and generally innate features of word-formation, proper to a particular language, are shown to be behind variation. Illustration is provided with examples from mainly Modern Greek, a fusional language which is rich in morphological structures and displays variation in the entire range of morphological processes. It is proposed that the examination of varying forms sheds light on the primacy of certain linguistic tendencies in a specific language and can give hints on possible linguistic changes.