The current book presents the theory, observations, mathematical modelling techniques, and applications of sea ice drift science. The theory is presented from the beginning on a graduate student level, so that students and researchers coming from other fields such as physical oceanography, meteorology, physics, engineering, environmental sciences or geography can use the book as a source book or self-study material. First the drift ice material is presented ending with the concept of 'ice state' - the relevant properties in sea ice dynamics. Ice kinematics observations are widely presented with the mathematical analysis methods, and thereafter come drift ice rheology - to close the triangle material - kinematics - stress. The momentum equation of sea ice is derived in detail and its general properties are carefully analysed. Then follow two chapters on analytical models: free drift and drift in the presence of internal friction: These are very important tools in understanding the dynamical behaviour of sea ice. The last topical chapter is numerical models, which are the modern tool to solve ice dynamics problem in short term and long term problems. The closing chapter summarises sea ice dynamics applications and the need of sea ice dynamicknowledge and gives some final remarks on the future of this branch of science.