Solution structures and hydrogen exchange characteristics of ligand-RNA aptamer and ligand-DNA aptamer complexes have been solved within the past year. The ligands range from cofactors to amino acids, nucleotides, aminoglycoside antibiotics and peptides that are targeted by the nucleic acid aptamers with high specificity and affinity. The structural and dynamics studies provide insights into the principles, patterns and diversity associated with nucleic acid architecture, molecular recognition and the adaptive binding that takes place upon complex formation. These new results provide opportunities for structure-based drug design strategies relevant to therapeutic intervention.