Monoliths have only recently shown promise as stationary phases in liquid chromatography (LC), and their chromatographic performance continues to improve as they are better understood and are supported by improved synthetic methods. They differ substantially in chromatographic bed structure from columns packed with particles, and they cannot be described rigorously by conventional chromatographic theory. Furthermore, column preparation is not generally as reproducible as for packed columns since stationary phase synthesis and chromatographic bed formation are accomplished at the same time instead of being optimized individually. This is expected to improve with experience.