Abstract： Due to the highly predictable long-term clinical outcomes, modern implant dentistry has become one of the most preferred treatment modalities for restoring missing teeth. However, the complications of implant therapy compromise the long-term implant success and remain a great challenge to clinicians. Hardware complications include the mechanical complications which are related to the manufacturer-fabricated components of the prosthesis, such as abutment/screw loosening, fracture and implant fracture; and the technical complication which are related to laboratory-fabricated components of the prosthesis, such as veneer chipping. The biological complications mainly include peri-implant mucositis and peri-implantitis. It is crucial to figure out how to effectively avoid and manage the complications of implant therapy. This article reported the definitions, incidences, risk factors, prevention and treatment of both mechanical and biological complications of implant therapy.