"Radical" templatic phonology is a template-based approach to segmental phonological representation. The central hypothesis is that the segmental phonological structure of words is represented as language-specific phonotactic templates, in the sense used in the developmental literature. Template-based organization of the early lexicon has been identified in children acquiring several different languages. It is the result of a usage-based abstracting or "induction" process based on both babbling practice (phonetic production) and input experience with specific adult phonological patterns. The resulting templates thus constitute patterns that reconcile (or 11 adapt") the model provided by target words with the child's own phonetic repertoire of syllables or word shapes - typically extending or building on the forms initially "selected" for first word production, in which adult and child forms show a close match. In adult phonology segment categories natural classes, or features - are best defined in terms of their occurrence in positions in the templates in individual languages, not as independent universal categories. After reviewing the status of segment categories and their phonetic basis in contemporary phonological theory we present crosslinguistic evidence of pervasive variation in both phonetic realization and phonological distribution patterns, evidence that supports the template construct.