Mature T- and natural killer (NK)-cell neoplasms comprise a group of morphologically, immunophenotypically, molecularly, and clinically heterogeneous disorders with generally unfavorable outcome. Results of first-line chemotherapy are unsatisfactory for the most common T-cell lymphomas (peripheral T-cell lymphoma, not otherwise specified; angioimmunoblastic T-cell lymphoma; anaplastic large cell lymphomas; anaplastic lymphoma tyrosine kinase-negative) as well as for many other entities. High-dose therapy followed by autologous hematopoietic stem cell transplantation (HSCT) is widely recommended for consolidation after a complete or partial remission is achieved. However, about one-third of patients never reach transplantation because of early relapse or refractoriness. Targeted therapies have recently been developed; combinations with chemotherapy may improve outcomes, but long-term results from prospective studies are largely missing. In this situation, allogeneic HSCT remains a valuable treatment option inducing long-lived remissions in about 30% to 50% of patients with relapsed and refractory T-cell lymphoma able to proceed to transplantation. Results of allogeneic transplantation for consolidation in first remission are less defined and its indications remain controversial. With growing evidence that haploidentical HSCT also works in lymphoma, more patients can be brought to transplantation. Decreasing the morbidity and mortality of allogeneic transplantation is a continuous challenge. Integrating new drugs into transplant concepts and setting up prospective studies involving allogeneic transplantation remain unmet needs that warrant urgent study in a group of disorders in which classical chemotherapy and new drugs have generated results, which are far from optimal until today.