Hybridization between closely related species, followed by back-crossing with the parental species, can lead to transfer of genetic material between established species, so-called introgression. Recent genomic investigations have revealed that this genetic transfer between species is far more common among animals than previously expected, and that even ancestral human populations have hybridized with related species such as Neanderthals and Denisovans. However, published claims of hybridization and introgression are based on a wide range of methodologies of which some provide more reliable results than others. In my talk, I will give an introduction to genomic methods used for the inference of hybridization, with a focus on phylogenetic approaches such as gene tree comparisons. I will demonstrate the application of these approaches with a case study on East African cichlid fishes of the genus Neolamprologus, which are well-known to hybridize when kept in the same aquaria. Based on whole-genome sequence data from five Neolamprologus species, we detected several past hybridization events, and found that large parts of the genomes of these species are affected by introgression.