The book "Programming Languages with Applications to Biology and Security" is a festschrift published in honor of Pierpaolo Degano on the occasion of his 65th birthday. It is based on a colloquium that took place in June 2015 in Pisa, Italy. Pierpaolo Degano has engaged with a variety of topics, including formal programming semantics, concurrency theory, systems biology, and security. This collection includes 22 peer-reviewed contributions as well as an extended abstract, featuring both personal memories and regular research papers from close collaborators and friends. Additionally, it highlights Degano's outstanding career and his significant scientific contributions. The included works address the central research themes that Degano has explored, as well as current issues in these fields.