Peri-implant diseases are plaque-associated pathologic condition characterized by the inflammatory process affecting hard and soft tissues around endosseous dental implants. These frequent complications are the result of an imbalance between the host response and bacterial challenge, which may affect the peri-implant mucosa “mucositis” or also involve the supporting bone “peri-implantitis”. Clinical aspects/signs of peri-implant diseases should be detected at each recall visit as well as swelling, erythema, bleeding on probing and suppuration. Moreover, many risk factors are involved in the development of peri-implant disease and most patients may have multiple risk factors including smoking, substance use disorders, socio-economic status, mental health disorders, old age and poor home dental care. In addition, iatrogenic, local, systemic, type of prosthesis and implant site-specific factors have been involved in the development of such complication. Clinicians must be aware of and recognizes the importance of such risk factors in order to manage them appropriately. This chapter aims to provide clinicians with an up-to-date understanding of peri-implant disease.