The invention provides novel non-β-lactam inhibitors of β-lactamases. In particular, the invention provides boronic acid-based compounds set forth in the specification. These compounds may be used with β-lactam antibiotics to bacterial infection, particularly, β-lactam-antibiotic-resistant bacterial infections. These compounds are also antibacterial agents by themselves. The invention further provides methods of using such compounds. Finally, the invention provides a pharmaceutical composition comprising these compounds.