Practicing metta is an ancient vocation in which we incline toward metta, toward a warm, expansive friendliness, each moment. In doing so, we also come to see what gets in the way of metta. A metta retreat offers us a focused period of training, helping us then to bring our metta more into our formal practice, our daily lives, and a world deeply in need of metta. Yet there are challenges in metta practice. We also identify a number of these challenges, and how responses to the challenges point to some of the fundamental ways that training in metta transforms us.