The primary aim of periodontal treatment is the long-term preservation of the periodontium. Before formulating a treatment plan, it is essential to assess the diagnosis, etiological factors, and the prognosis of the remaining teeth while considering the anticipated functional and esthetic outcomes. A long-term prognosis of the affected teeth should be meticulously evaluated during the treatment planning phase, particularly when periodontal therapy is combined with extensive oral prosthetic rehabilitation or dental implant placement. Establishment of single tooth prognosis is based on multiple patient and tooth-related factors. Various classifications have been suggested; however, the distinctions between the different stages or categories, especially in the borderline cases, can sometimes be ambiguous. Patient-related factors influencing tooth prognosis include age, systemic health, personal and familial history of periodontal disease, oral hygiene practices, compliance with recall visits, smoking habits, parafunctional habits, and the patient’s desire to retain their teeth. Tooth-related factors include the number of remaining teeth, the extent of clinical attachment loss, degree of bone loss, the configuration of bone defects, furcation involvement, tooth mobility, crown-to-root ratio, caries or endodontic involvement, root defects, tooth position, root proximity, prior rehabilitation, the type of periodontal therapy administered, the clinician’s expertise, and the tooth’s strategic importance and treatment alternatives. Evidence-based decision-making is fundamental, requiring the use of current research to guide patient care, thus bridging the gap between clinical research and actual practice. However, while evidence-based dentistry integrates the best available research with clinical skills and patient preferences, it serves to inform, rather than replace, clinical judgment. This chapter will examine all factors associated with tooth prognosis and propose a framework to aid in prognosis determination for individual cases. Treatment alternatives must be methodically considered for each case, as extraction of teeth due to periodontal reasons often necessitates significant bone augmentation for implant therapy. Moreover, periodontal patients may be at increased risk for peri-implant diseases and implant failure. Consequently, the associated morbidity, duration, and likelihood of overall long-term success should be carefully considered before the route of periodontal therapy is abandoned.