With the latest relativistic heavy-ion collision experiments at RHIC and the LHC the study of the strongly-interacting matter in extreme conditions has entered its golden era. The understanding of the various phenomena observed in the data as well as their connections to the underlying physical properties of the system requires a broad and interdisciplinary knowledge. In this course we will develop basic concepts, models and frameworks including some elements of statistical mechanics, relativity, thermodynamics, fluid dynamics and kinetic theory relevant for such an understanding.