This chapter fi rst discusses normal variants in the knee and lower leg, covering topics such as distal femoral epiphyseal ossifi cation variants, benign cortical defects, cortical desmoids, tibial tuberosity development, and growth recovery lines. Variants of the fabella, patella, and patellofemoral articulation are discussed, as well as both congenital and developmental patellar instability. The chapter then presents congenital limb anomalies such as femoral bifurcation and duplication, longitudinal defi ciency of the tibia, and longitudinal defi ciency of the fi bula. Bowing and alignment disorders follow, with sections on various forms of tibial and fi bular bowing, and knee dislocation and hyperextension. Discussion of aberrant alignment includes physiological bowing, infantile tibia vara, rickets, genu valgum, and long bone rotational abnormalities. The chapter concludes with a discussion of leg-length discrepancy.Variable osseous development leads to a changing appearance of the bones of the lower extremity during childhood. In order to recognize pathology, it is important to understand the ranges of normal. Developmental abnormalities of the lower extremity have a wide range of severity and can have signifi cant impact on patient function.