This volume includes fifteen research papers to celebrate Luiz Carlos Pereiras 60th birthday. Among the authors contributing to the volume we find colleagues, friends - including his PhD advisor - and admirers. Similar to Luiz Carlos Pereiras intellectual interests and work, the contributions range from Philosophy to Mathematics, from Mathematics to Logic, and from Logic to Philosophy, passing through Computer Science. They are the result of current research by well-known scholars in these fields. Proof Theory is, maybe, the Ariadnes thread that unite the different subjects treated. Questions...