Over the last several decades increasing attention has been paid to minimising injuries to people inside a structure that experiences an impact, as well as alleviating the effect of an impact on a structure. This has led to significant research being carried out into the design and development of energy absorbers in order to mitigate the adverse effects of an impact and to increase the safety of a structure. Energy absorbers have found common application in the automobile, nuclear, spacecraft, and aircraft industries. This work presents the energy absorption response and crashworthiness optimisation of thin walled single and nested tubes under quasi-static and dynamic lateral loading. The primary aim of this study was to conduct investigations into the above systems and thus, where applicable, employ them in crashworthiness applications and energy absorption systems. Two different configurations of energy absorbing mechanisms were studied in this thesis. The first type was a single tube, the geometrical profile of which was varied in order to study its absorption characteristics. In an attempt to enhance the energy absorption capacity of a single tube, internally nested tubes were also examined as energy absorbers. This nested system formed the second configuration. Due to strain localisation around the plastic hinges, external constraints were employed to increase the number of plastic hinges and thereby increase the volume of material reaching plasticity. Various indicators that described the effectiveness of an energy absorbing mechanism were used as markers to compare the various systems. Detailed finite element models, validated against experiments and existing experimental and numerical results, were developed using both the implicit code (ANSYS) and explicit code (ANSYS-LSDYNA) to assess the energy absorption responses and deformation modes. Response surface methodology (RSM) was employed in parallel with the finite element models to perform both parametric studies and multi-objective optimization in order to establish the optimal configurations for the various mechanisms proposed in this study. Major findings show that the energy absorption response can be effectively controlled by varying geometric parameters such as diameter, thickness, and width.