The first clause of Cal. Welf. & Inst. Code 300(b)(1) authorizes a juvenile court to exercise dependency jurisdiction over a child without a finding that a parent is at fault or blameworthy for her failure or inability to supervise or protect her child. The court of appeal also concluded that section 300(b)(1)’s first clause does not require such a finding. In this case, the Los Angeles County Department of Children and Family Services filed a petition to declare then seventeen-year-old R.T. a dependent of the juvenile court on the ground that she faced a substantial risk of serious physical harm or illness as a result of Mother’s failure or inability adequately to supervise or protect her. The juvenile court asserted jurisdiction over R.T. The court of appeal affirmed the jurisdictional and dispositional orders of the juvenile court. The Supreme Court affirmed, holding that when a child’s behavior places her at substantial risk of serious physical harm and a parent is unable to protect or supervise that child, the juvenile court’s assertion of jurisdiction is authorized under section 300(b)(1).