High tibial osteotomy (HTO) is a widely performed procedure, and good results can be achieved with appropriate patient selection and precise surgical technique. Clinical indications include varus alignment of the knee associated with medial compartment arthrosis, knee instability, medial compartment overload following meniscectomy, and osteochondral defects requiring resurfacing procedures. Coronal alignment (ie, varus, valgus) and sagittal alignment (ie, tibial slope) should be thoroughly evaluated in all cases. Many techniques have been described for HTO, whether alone or in combination with other procedures (eg, anterior cruciate ligament reconstruction, meniscal transplant, cartilage resurfacing). Little direct evidence exists regarding the effectiveness of HTO alone or in combination with other procedures because of the lack of randomized controlled studies. However, it is commonly accepted that correct alignment is essential in achieving durable results.