This book provides an overview of the initiation of combustion processes of polymeric materials. It presents physicochemical processes associated with heating as well as numerical methods for initiation parameter calculation. In addition, the book describes thermal degradation of polymers and the effect of an incident heat flux on initiation time. It then highlights the most commonly used devices for measuring the time to ignition using external heat sources. The target group of this book are scientists and researchers dealing with materials combustion and also graduates and practitioners focused on fire protection.