Electronic Journal of Differential Equations, Vol. 2010(2010), No. 144, pp. 1-20. Title: Transport equations in cell population dynamics I Author: Mohamed Boulanouar (Univ. de Poitiers, France) Abstract: In this article, we study a cell proliferating model, where each cell is characterized by its degree of maturity and its maturation velocity. The boundary conditions in this model generalize the known biological rules. We consider also the degenerate case corresponding to infinite maturation velocity. Then we show that this model is governed by a strongly continuous semigroup and give its explicit expression. Submitted May 23, 2010. Published October 12, 2010. Math Subject Classifications: 92C37, 82D75. Key Words: Semigroups; operators; boundary value problem; cell population dynamic; general boundary condition.