A combined experimental and numerical approach is adopted to investigate fracture processes in concrete. The experimental programme focuses on the failure of concrete subjected to mixed mode I and II loading. The influence of shear load on the nucleation and propagation of cracks in concrete is studied by means of four-point-shear tests on single and double edge notched beams. A numerical model for simulating fracture is developed in which the heterogeneous microstructure of concrete is implemented. The model is used to carry out simulations of different fracture experiments. In Chapter 1 of this report the subject of the investigation is clarified. Chapter 2 deals with a summary of research regarding tensile fracture and combined tensile and shear fracture of concrete. An overview of different types of experiments is given. Furthermore numerical models and simulations of fracture tests are discussed. The experiments conducted in the present investigation are described in Chapter 3. Beam specimens with one or two notches, made of different concrete mixes are loaded in fourpoint- shear. All experiments are carried out under displacement control using a closed loop hydraulic system. In the developed test set-up experiments can be carried out either with freely rotating or fixed supports. The results of the various experiments are presented in Chapter 4. The experimental outcome is presented by means of crack patterns, different load-deformation curves and details of cracks obtained with an optical microscope. In Chapter 5 the numerical model is explained. Different ways of implementing heterogeneity are presented. The determination of the various input parameters is discussed. Simulations of different types of experiments are presented in Chapter 6, i.e. uniaxial tensile tests, four-point-shear tests, pull-out of anchor bolts and mixed mode tests on plate specimens. The last chapter includes a discussion of the results and a summary of the conclusions. The main conclusion derived from the experimental part of this investigation is that fracture in concrete is a mode I mechanism, even if the external loading on a specimen is a combination of tensile and shear. The numerical model developed has proved able to predict fracture in concrete quite accurately. Simulations with the model increase insight into the fracture mechanism.