Complete removable dental prostheses are effective for replacing missing oral structures in edentulous patients but have limitations, particularly in restoring function. Dental implants have emerged as a superior alternative, especially for mandibular overdentures (IOD). IODs can be designed according to individual needs and anatomic factors, by using varying numbers and positioning of implants, as well as selecting the most appropriate anchorage system. The different design concepts available for the maxilla and the mandible, concerning the number and position of implants are reviewed. The mechanisms of the anchorage systems available are described and their specific indications are discussed. IODs are widely recognized as a highly effective and predictable treatment for edentulous patients, offering improved oral function, comfort, and quality of life, associated with high implant and prosthetic survival and success rates. These benefits have been confirmed for the various treatment concepts described in this review, concerning both the treatment of the maxilla and the mandible. Differences in clinical, peri-implant radiographic, or prosthetic parameters, as well as in patient-reported outcomes, such as satisfaction, are minimal between treatments, when present. Long-term use of IODs is associated with a variety of biological and mechanical complications, as well as the need for continued maintenance. Mechanical issues are among the most frequently encountered events in IODs. Most commonly, they involve gradual loss of retention due to wear, but can also include attachment loosening, detachment or wear of the metal housing, fracture of the acrylic denture base, denture relining, adjustments due to mucosal sore spots or even fracture/loss of the prosthetic teeth. Limited evidence was found regarding the factors that predispose implant overdentures to mechanical complications. Concerning biological complications, they mainly include peri-implant mucositis and peri-implantitis. Known risk factors for periimplantitis include inadequate plaque control, insufficient access around prosthetic elements for correct hygiene, systemic conditions such as diabetes, and smoking. Despite the effectiveness of IODs, many patients—especially the elderly or medically compromised—are still treated with conventional dentures due to barriers like cost, fear of surgery, or health concerns. There is a growing demand for developing minimally invasive and cost-effective solutions in implant therapy. More recent research focuses on simplifying treatment through minimally invasive surgical procedures, such as reducing the number of support implants (single-implant mandibular overdentures (SIMOs)), or reducing the need for bone augmentation procedures by reducing implant diameter or length. This narrative review focuses on treatment outcomes, patient-reported outcomes, and clinical protocols of removable implant overdentures and aims to present areas of future research focus where a knowledge gap is still present.