This book is concerned with the automatic generation of inheritance hierarchies for the level below the phoneme and their application in acoustic modelling for automatic speech recognition. Over the last decade computational phonology has adopted the typed feature structure representation formalism while paying little attention to subphonetic feature structures. Similarly paradigmatic phonological knowledge used in acoustic modelling does usually not go beyond phonological feature bundles. Here the discrepancy between hierarchicallystructured lexica as they are promoted in computational phonology and the flatstructured feature bundles common in acoustic modelling is addressed in a powerful framework for solving combinatorial problems i.e. constraint programming.