CLL is an incurable disease with current therapies. Modern chemoimmunotherapies, including combinations of rituximab and purine nucleoside analogues (fludarabine, cladribine, and pentostatin), offer the possibility for improved survival, but all patients will eventually relapse. Patients with relapsed or refractory disease will only experience diminishing benefits with additional lines of therapy. In addition, patients with high-risk CLL have poor responses to even first-line therapies. Lenalidomide and dasatinib have non-overlapping proposed mechanisms of action. Single agent phase II studies with lenalidomide and dasatinib have demonstrated responses in heavily pretreated and high-risk patients. For these reasons, we propose to treat patients with relapsed and/or refractory CLL to purine nucleoside analogue therapy with combination lenalidomide and dasatinib.