Many industries use safety-critical systems and software, the failure of which may result in the loss of human lives. This article investigates the development and certification of safetycritical software, with a focus on the avionics industry. It highlights the problems encountered in companies to demonstrate compliance with the certification requirements and indicates current industrial practices. It demonstrates the interest and importance of closely and continuously integrating certification requirements in the software development process. It underlines a very recent trend in industry that consists in taking inspiration from agile principles in order to ensure that certification requirements applicable to software development are met as early as possible. It presents some successful industrial experiments and concludes on practical lessons that could be transferred to other projects.