IntroductionA dynamical system is called positive if its trajectory starting from any nonnegative initial condition state remains forever in the positive orthant for all nonnegative inputs. An overview of state of the art in positive system theory is given in the monographs [7,10] and in the papers [11][12][13][14]. Models having positive behavior can be found in engineering, economics, social sciences, biology and medicine, etc. The Lyapunov, Perron and Bohl exponents and stability of time-varying discretetime linear systems have been investigated in [1][2][3][4][5][6][7][8][9]. The positive standard and descriptor systems, and their stability have been analyzed in [13][14][15][16]. The positive linear systems with different fractional orders have been addressed in [14,17] and the singular discrete-time linear systems in [15].In this paper the positivity and asymptotic stability of the time-varying discretetime linear systems will be investigated.The paper is organized as follows. In section 2 the solution of the state-equation describing the time-varying discrete-time linear system is derived and necessary and sufficient conditions for the positivity of the systems are established. The asymptotic stability of the positive systems is addressed in section 3, where conditions for the stability are proposed. Concluding remarks are given in section 4.The following notation will be used:-the set of real numbers, -the set of real matrices, -the set of matrices with nonnegative entries and , -the identity matrix.