This study addresses the question of what basic principles and constraints govern blending while focusing on the description and analysis of phonological properties of Korean blends. Korean blending shows a systematic phonological word-formation process that usually preserves the prosodic structure of the head source word, while the initial part of the segmental sequence of the blend is from the non-head source word. This general pattern can be explained by adopting prosodic faithfulness constraints for the head and segmental faithfulness constraints for both source words. Usually, prosodic faithfulness overrides segmental faithfulness. General and exceptional patterns of Korean blends can be explained by the interaction of prosodic faithfulness and segmental faithfulness constraints within the framework of Harmonic Grammar.