This document provides an overview of lexicology and word formation. It discusses the key concepts in lexicology including definitions of lexicology, words, and word groups. It then describes the main ways that new words are formed in English: affixation, composition, conversion, and abbreviation. Affixation, specifically prefixation and suffixation, are described as highly productive ways of word formation by adding affixes to roots to derive new words. The semantics and functions of affixes are also discussed.