Formal youth mentoring programmes are based on the belief that positive relationships with adults can support young people in their emotional, cognitive and identity development into adulthood. The aim of this chapter is to consider the evidence to support the value of formal youth mentoring in general and its use for children in care specifically. In the first section, a comprehensive review of the research relating to formal mentoring is provided. In the second section of this chapter, the focus is on mentoring specifically for children in care. We draw from three main sources for this section: findings relating to general mentoring that apply across populations including children in care; intensive mentoring for young people with higher levels of need or risk and special projects aimed at youth mentoring for children in care and those transitioning out of care. Overall, we see that there is a dearth of detailed studies of young mentoring specifically for children in care. Following this, we summarise findings relating to the challenges involved in formal youth mentoring for young people in care. Many of these focus on the complexity of the issues arising for the young person as well as the practice challenges of placement moves, time and sustainability of relationships. In our conclusion, we note that some of these challenges are shared with natural mentoring and others are specific to formal mentoring.