Title: Adapt-to-Learn: Policy Transfer in Reinforcement Learning. Abstract: Efficient and robust policy transfer remains a key challenge in reinforcement learning. Policy transfer through warm initialization, imitation, or interacting over a large set of agents with randomized instances, have been commonly applied to solve a variety of Reinforcement Learning (RL) tasks. However, this is far from how behavior transfer happens in the biological world: Humans and animals are able to quickly adapt the learned behaviors between similar tasks and learn new skills when presented with new situations. Here we seek to answer the question: Will learning to combine adaptation reward with environmental reward lead to a more efficient transfer of policies between domains? We introduce a principled mechanism that can \textbf{``Adapt-to-Learn"}, that is adapt the source policy to learn to solve a target task with significant transition differences and uncertainties.  We show through theory and experiments that our method leads to a significantly reduced sample complexity of transferring the policies between the tasks.