Youth-onset type 2 diabetes (YO-T2D) is typically defined as type 2 diabetes (T2D) diagnosed before the age of 20 or 25 years. The incidence of YO-T2D has risen steadily over the past several decades in line with rising childhood obesity. The complex pathogenesis of T2D involves β-cell dysfunction, insulin resistance, and variable dysfunctions of the adipose tissue, the skeletal muscle, and the liver. Certain ethnic backgrounds appear to convey increased risk for YO-T2D, potentially related to underlying genetic differences contributing to reduced insulin secretion and/or increased insulin resistance. Youth from minoritized groups and under-resourced backgrounds are more likely to present with YO-T2D, and the mechanisms underlying this association are currently unknown. Current guidelines recommend risk-based screening for T2D after the onset of puberty or at 10 years of age, whichever is earlier, and for children with overweight or obesity and at least one of the risk factors discussed in this chapter. Lifestyle modification remains an important component of treatment following the diagnosis of T2D in youth despite the availability of pharmacologic and surgical therapies.