The ever-increasing number of drug-resistant bacteria is a major challenge in healthcare and creates an urgent need for novel compounds for treatment. Host defense antimicrobial peptides have high potential to become the new generation of antibiotic compounds. Antimicrobial peptides constitute a major part of the innate defense system in all life forms. Most of these cationic amphipathic peptides are often unstructured in isolation but readily adopt amphipathic helical structures in complex with lipid membranes. Such structural stabilization is primarily responsible for the membrane permeation and cell lysis activities of these molecules. Understanding structure–function correlations of antimicrobial peptides is critical for the development of nontoxic therapeutics. In this minireview, we discuss atomic-resolution NMR structures of two highly potent helical antimicrobial peptides, MSI-78 and MSI-594, providing novel insights into their mechanisms of action.