Sex determination evolution in teleost fishes is amazingly dynamic with coexistence of both environmentally and genetically-driven sex determination systems. In species with genetic sex determination, both classical male (XX-XY) and female (ZZ-ZW) heterogametic systems can be found in closely related species, and even sometime in different populations of the same species. There are also species with more complex genetic sex determination systems relying on polygenic sex determination with or without multiple sex chromosomes. In addition, master sex determining genes controlling the genetic sex determination gene network, and in fine the individual sexualization, are also subject to frequent changes. This presentation will focus on how new genomics resources (genome and transcriptome assemblies), tools (sequencing methodologies, bioinformatics) and approaches (whole genome sequencing, RAD-sequencing, Pool-sequencing) have deeply changed the sex determination research field and how they can be used to better understand the amazing diversity of sex chromosomes and master sex determining genes. Examples will be taken from diverse clades of teleost fishes to illustrate the frequent turnovers of sex determination systems, the variability of sex chromosome differentiation, and the diversity of master sex determining genes and their related mechanisms of action. We will also report on recent results showing that supernumerary B chromosomes can drive sex determination in some fish species and thus could be considered as a new class of unusual sex chromosome (B-Sex).