Since the 1960s, osseointegration has become a routine method for treating partial and total edentulism. Dental implants are commonly used in clinical situations to replace natural teeth. Despite numerous advances in implant materials, techniques and design, implant failures do occur and implants have to be removed. Implant failures can be divided into early failures (failure to achieve osseointegration) and late failures (failure to maintain osseointegration). Early failures occur during the healing period or when the abutments are connected, whereas late failures occur after the implants have been loaded. Peri-implantitis and lack of osseointegration are considered to be the main factors leading to implant failure. Other causes include occlusal overload, the patient's medical condition, smoking and implant characteristics. The aim of this paper is to discuss the different aetiologies of implant failure described in the literature.