Eosinophils have long been associated with allergy and parasitic infections. Today, they are considered as multifunctional leukocytes, which participate both in innate and adaptive immune response though the expression of various receptors and mediators. Although the tumor-associated eosinophilia is observed for a long time in many hematological and solid malignancies, with a generally good prognosis value, there is a lack of knowledge on the different mechanisms involved in this phenomenon. Moreover, the recent discovery in human eosinophils of different receptors and mediators, shared with lymphocytes and involved in anti-tumor defense, suggests that eosinophils can play a role in anti-tumoral immunity. We review in the present paper the current knowledge on epidemiology, recruitment, and mechanisms involved in the response of eosinophils toward tumors.