The purpose of this book is to describe the rules that regulate the institute of whistleblowing in the public sector, detailing the applicable laws, and the main guarantees and characteristics as a means of citizen participation, a duty of public officials and an instrument in the fight against public corruption. This is of interest both for potential whistleblowers, whether citizens or public officials, as well as for the bodies and officials in charge of receiving and processing them in order to carry out this task in accordance with the legal system. For this purpose, we resorted to the national and international regulations in force that allow us to conclude that although the whistleblower is a figure integrated in our legal system, we still have pending challenges in terms of greater guarantees to the whistleblower and speed in its investigation.