This book devoted to the analysis of SBVP¿s for ODE¿s with a singularity of the different types. Also, discussion three main questions: existence and uniqueness of solutions, behavior of the solution in the neighborhood of the singular points and its numerical approximation. Many examples are presented to demonstrate the applicability and efficiency of the methods on one hand and to confirm the convergence order on the other hand, two applications in physiology are presented and the results are compared with the conventional methods. Also, a class of SBVP¿s modeling the heat conduction in the human head is studied.