Flatfoot is a condition in which the medial longitudinal arch is flat and with weightbearing the entire sole rests on the ground. Pes planus refers to the same condition, pes a Latin word meaning foot and planus meaning flat. Flexible flatfeet occur in both children and adults. Flatfoot deformit results of a combination of many structural factors. Flatfoot can be categorized as rigid or flexible. Flexible form has no single identifiable cause and is often asymptomatic. It may become painful and may require intervention. Treatment modalities include rest, physiotherapy, orthotics and anti-inflammatory medications. Understanding the radiographic findings is important when trying to assess the severity of a flatfoot deformity. Surgery is uncommon unless pain persists in spite of nonsurgical treatment. Surgical options include soft tissue procedures, realignment osteotomies and Subtalar arthroereisis. Subtalar arthroereisis as an adjunct procedure may hold promise for patients who have mild and more severe variants of posterior tibial tendon dysfunction (PTTD). The biomechanics of the implant function have not been fully elucidated, and questions remain about the best clinical indications. This article aimed to review flexible flatfoot and the using of Subtalar arthroereisis technique for the treatment of flexible flatfoot.