This article has two goals: descriptive and theoretical. On the descriptive side, the article presents a grammar of gliding and epenthesis of Upper Sorbian. The descriptive goal is worthy because Upper Sorbian has a highly complex but regular and productive system of gliding and epenthesis. Upper Sorbian stands out from a typological point of view because it has ten [sic] different strategies to satisfy Onset.

On the theoretical side, the question is whether Optimality Theory that has been designed to solve conspiracies can deal with the complexities of Upper Sorbian. The answer is that it cannot unless it is modified to admit derivational levels. A point of interest is that level 1 in Upper Sorbian must be defined as the root level, not as the expected stem level that includes roots and affixes. Further, it is demonstrated that Itô and Mester’s Crisp Edge constraint makes wrong predictions for Upper Sorbian, so a new constraint, Multi, is postulated. Also, the analysis bears on the issue of positional markedness versus positional faithfulness and the question of whether Duke of York derivations should be admitted in phonology.