In this PhD thesis an Isogeometric Boundary Element Method (IGA-BEM) for three dimensional steady lifting flows based on Morino's [50] formulation is presented. A potential flow assumption is used and the unknown perturbation potential satisfies Laplace's equation. Application of Green's identities leads to a Boundary Integral Equation (BIE) that is enhanced with kinematic and dynamic boundary conditions. Analysis suitable T-splines are used for the representation of all boundary surfaces and the unknown perturbation potential is approximated by the same T-spline basis as the one used for the geometry. The BIE is discretised by enforcing it on the generalised version of Greville points for unstructured T-meshes. A novel numerical application of the so-called Kutta condition is introduced that utilises the advantages of IGA with regard to the smoothness of the trailing edge curve basis functions. This leads to a quadratic system that is solved by a Newton-Raphson iterative scheme. The method is applied for three different test cases and shows good agreement with existing experimental results and superior behaviour when compared to a low order panel method. The effect of the tip singularity on Kutta condition is also investigated for different levels of refinement and positions of the trailing edge collocation points.