All cell types from the testis can give rise to neoplasms. It is of relevance to distinguish germ cell tumors and non-germ cell tumors. Understanding the existence of the various types of neoplasms of the testis, and getting insight into their pathogenesis, requires knowledge about the normal anatomy and physiology of both the developing and mature testis. The germ cell tumors represent the most frequent neoplasm, followed by the sex cord-stromal tumors (Leydig cell and Sertoli cell tumors), and others (lymphoma, etc.). Based on morphological criteria, germ cell tumors are subdivided into (classic) seminoma, spermatocytic seminoma, embryonal carcinoma, yolk sac tumor, teratoma, and choriocarcinoma. Alternatively, a classification system has been proposed, in which age at presentation, pattern of genomic imprinting, cell of origin, chromosomal constitution, as well as representative animal model(s) are included. Within the testis, three of these subtypes can be found, each with their own clinical and pathological characteristics. Based on this recognition, an informative set of diagnostic markers has been developed, proven to be of value in a clinical setting. These can even be applied for early diagnosis, i.e., in the pre-invasive stage, in specific groups of individuals known to be at risk. This will possibly prevent the need for systemic treatment, irradiation, or chemotherapy at a relatively young age, known to have significant side effects.