Affix productivity in Modern English represents a dynamic aspect of morphological development, reflecting both linguistic innovation and functional necessity. Derivational and inflectional affixes contribute significantly to word formation, enabling the language to expand its lexicon efficiently. Among the most productive affixes are -ness, -er, -less, and -ize, which continue to generate new lexical items in contemporary usage. The degree of affix productivity varies based on frequency, semantic transparency, and the openness of lexical categories they attach to. Productive affixes tend to be more flexible and are often used in neologisms and informal contexts. Recent linguistic studies have shown that technological, social, and cultural changes heavily influence affix usage and productivity rates. Furthermore, corpus-based approaches help quantify affix productivity and track morphological trends in real-world data. Understanding affix productivity is essential not only for morphological theory but also for practical applications in lexicography, language teaching, and natural language processing.