This is the first book devoted to the positive multivariable 1D and 2D linear, time-invariant, finite-dimensional system. The book is based on the Author's lectures for Ph.D. students, delivered at Warsaw University of Technology in the academic year 1999/2000. The book consists of two parts; the first part is devoted to the 1D positive linear systems and the second to the 2D positive linear systems described by the Rosser model and the Fornasini-Marchesini models. Definitions, basic properties and theorems concerning positive matrices and graphs are presented; the externally and internally positive linear continuous-time and discrete-time linear systems are considered; the reachability, controlability and observability of positive linear systems are discussed. The realisation problem for positive 1D and 2D systems is considered, and the 2D models of externally and internally positive and their properties and controllability and minimum energy control of positive 2D systems are investigated.