Spermatogenesis is an intensely regulated process of germ cell development which takes place in the seminiferous tubules of the testis. In addition to known endocrine and autocrine/paracrine signaling pathways, there is now strong evidence that direct intercellular communication via gap junction channels and their specific connexins represents an important mechanism in the regulation of spermatogenesis. Another possibility is that connexins may indirectly regulate the spermatogenic process through modulation of tight and adherens junction proteins, further main structural components of the Sertoli-Sertoli junctional complexes at the blood-testis barrier site. The present review is focused on connexin 43 and updates its possible roles and functions in testicular junction dynamics and in the initiation and maintenance of spermatogenesis. In addition, testicular phenotypes of recently generated (1) conventional connexin 43 knockout mice, (2) connexin 43 knockin mice and (3) transgenic mice exhibiting a cell-specific (conditional) connexin 43 knockout will be discussed.