Cementitious materials are brittle and have an inherent weakness in resisting in tension. Fibre reinforcement is an effective means of enhancing the fracture characteristics of concrete. The use of low fibre volume fractions in concrete has increased significantly in recent years for the control of opening and slippage of concrete cracks. To understand fully such effects of fibres in concrete, it is important to assess their effects on the various fracture mode of concrete. This study looks at the performance of discrete end-hooked and straight steel fibres crossing a cracking plane at various angles loaded normal to the plane. In addition to discrete fibre tests, uniaxial tension tests are conducted on the dog-bone shaped specimens containing randomly distributed fibres with fibre volumes of 0.5%, 1.0%, 1.5% and 2.0% with end-hooked only and hybrid steel fibres combinations. X-ray imaging is used to investigate the mechanisms of fracture in fibre reinforced concrete and to identify the shape of the discrete fibres at various stages of loading and quantitative mapping of snubbing regions. An increase in fibre volume concentration can have an adverse effect on the tensile performance of a fibre reinforced composite when very high strength, end-hooked, fibres are used in a matrix of moderate strength. The experimental investigation showed that an increase in fibre volume concentration can lead to a decreased in the proportion of end-hooked fibres straightening through the end-hook. In this case, failure of the matrix surrounding the hook follows and significantly influences the behaviour. A relationship between fibre and matrix mechanical properties is developed and the result supports the findings obtained from the tests conducted in this study. X-ray imaging was also undertaken on dog-bone specimens under load. The tests were used to map the cracks around and through the fibre and a statistical model developed to determine fibre distribution. The experimental results of discrete fibre tests and results of digital X-ray image analysis are incorporated in the development of a behavioural model known as the Unified Variable Engagement Model. The model is validated against data from the literature and within this study, and a good correlation observed.