The purpose of the sixth edition, which is fully adapted to the International System of Units, is to present a comprehensible and well-documented approach to the finite element method, suitable for both undergraduate and postgraduate students. The book is written to serve as the primary "tool" for undergraduate civil and mechanical engineering students, who will primarily deal with stress analysis and heat transfer, but it also covers topics related to fluid flow in porous media and through hydraulic networks, electrical networks, and electrostatics. The concepts are presented in a simple form and are accompanied by many problem examples. The book presents the theoretical background and the most basic handling methods for the following topics: simple springs and rods, two-dimensional and three-dimensional truss analysis, beam bending, plane frame analysis, grid, and space frame simple plane stress/strain elements, leading to more complex plane stress/strain elements, and their applications axisymmetric stress analysis isoparametric formulation of the finite element method three-dimensional stress analysis plate bending analysis heat and mass transfer fluid flow through porous media and around solid bodies, hydraulic networks, electrical networks, and electrostatic analysis thermal stress analysis time-dependent stress and heat transfer problems Additionally, the book includes appendices with material on: matrix algebra, methods for solving systems of equations, elasticity theory, nodal forces of equivalent work, and the principle of virtual work. The book contains more than 100 solved examples for better understanding of the theory, while at the end of the chapters more than 570 problems are provided for solution. At the end of the book, answers to many of these are included. Book contents: •Introduction •Introduction to the stiffness (displacement) method •Development of truss equations •Development of beam equations •Frame and grid equations •Development of plane stress and plane strain stiffness equations •Practical issues of simulation, interpretation of results, and examples of plane stress/strain analysis •Development of linear strain triangle equations •Axisymmetric elements •Isoparametric formulation •Three-dimensional stress analysis •Plate bending element •Heat and mass transfer •Fluid flow in porous media and through hydraulic networks; electrical networks and electrostatics •Thermal stress •Structural dynamics and time-dependent heat propagation •Appendices Scientific editing of the Greek edition:  Georgios E. Stavroulakis, Technical University of Crete