This book constitutes the refereed proceedings of the 21st Brazilian Congress on BioInformatics, X-Meeting 2025, held in João Pessoa, Brazil, during June 3-6, 2025.

The 14 full papers and 2 short papers included in this book were carefully reviewed and selected from 35 submissions. These papers present ongoing research on Bioinformatics, as well as their application in a number of diverse areas such as DNA and Genomics, RNA and transcriptomic, Proteins and Proteomics, Database and Software Development, Phylogeny and Evolution, Systems Biology and Modeling, among others by considering applications on health, agriculture and microorganism and plants.