This paper proposes a set of constraints within the framework of Optimality Theory that accounts for syllable-final laryngeal neutralization and voicing assimilation in obstruent clusters. The interaction of positional faithfulness and markedness is shown to result in laryngeal neutralization. Regressive assimilation is shown to be a result of the interaction of positional faithfulness with a constraint preferring adjacent obstruents to agree in voicing. Rerankings of the proposed constraints account for attested patterns of voicing assimilation and neutralization: unlike previous neutralization and spread analyses, this approach makes the correct prediction that it is equally natural for voicing assimilation in clusters to combine with either devoicing of or retention of voicing distinctions in word-final consonants. It is argued that the interactions of these constraints account for why voicing assimilation is always regressive unless special circumstances hold.