One of the most common failure modes in composite structures is delamination of the layers. Delamination damage is significant in terms of the stiffness of the composite structure, unlike matrix cracks which may go unnoticed. It was decided to investigate the recovery of mechanical properties after delamination damage. In this PhD the influence of delamination on the stiffness of the composite structure was investigated. The most favourable values of the technological parameters which give the highest self-healing effect were determined. A series of experiments were carried out to assess the effectiveness of self-healing in recovering mechanical properties. A novel PMMA-based resin was used for the self-healing ivestigation. The mechanical properties of composites with a thermoplastic matrix can be recovered by applying pressure for a certain period of time at temperatures above glass transition. The developed methodology can recover up to 88% of the initial mechanical property level. A methodology has also been developed in this work to identify the interlaminar strength and delamination energy parameters of a composite laminate for modelling delamination damage using the finite element method. A finite element model has been developed to predict the occurrence, propagation and influence of delamination failure on the residual strength of the laminate in laminated composite laminates.