Solid tumors are composed of malignant cells surrounded by a tumor-conditioned stroma that contains extracellular matrix and a variety of nonmalignant populations, including myeloid cells, lymphocytes, fibroblasts, and endothelial cells. These stromal elements form a local immunoregulatory network that must be overcome to achieve eradication of established tumors by immunotherapy. On March 21-22, 2012, a symposium was held in Pamplona, Spain, to share the recent advances regarding the molecules and cells that create and sustain this immune-hostile tumor microenvironment. Excellent targets for immunotherapeutic intervention were identified, and a number of therapeutic strategies under translation from mouse to human were presented.