This textbook gives a unified treatment of the solution of various linear equations that arise in science and engineering with examples. It is based on a course taught by the first author for over thirty years. Some unique features include: Use of symbolic software for illustrating and enhancing the impact of physical parameter changes on solutions. Multi-scale analysis of engineering problems with physical interpretation of time and length scales in terms of eigenvalues and eigenvectors/eigenfunctions. Discussion of compartment models for various finite dimensional problems. Evaluation and illustration of functions of matrices (and use of symbolic manipulation) to solve multi-component diffusion-convection-reaction problems. Illustration of the techniques and interpretation of solutions to several classical engineering problems. Emphasis on the connection between discrete (matrix algebra) and continuum. Physical interpretation of adjoint operator and adjoint systems. Use of complex analysis and algebra in the solution of practical engineering problems.