This dissertation examines the palatalization of consonants in historic and living dialects of three West-Germanic languages: Dutch, German, and Frisian. Palatalization was a common feature of the West-Germanic phonological system and can be found in some form in all West-Germanic languages of the present. It is argued that the extent of its presence and its importance in the development of West-Germanic phonology has been underestimated, and that it played a central role in the rise of i-umlaut. In the first chapter, the term palatalization is defined and the most important research problems in several areas, including phonological theory, historical linguistics, paleography, and dialectology, are outlined. The dissertation dis-cusses the terms that have been in use in different traditions for consonant palatalization (especially German Mouillierung and English palatalization and the problems created by the fact that the modern term palatalization encompasses several related phenomena. The different treatments of consonant palatalization in phonological theories of the past century are examined; weaknesses in the description of palatalization within current theoretical frameworks are noted. Chapters 2, 3, and 4 discuss the existence and role of consonant palatalization and palatal(ized) consonants in the past and present dialects of Dutch, German, and Frisian, respectively.