[Author's abstract] The prevention of ice on aircraft components is critical to aircraft performance and operation. Even small amounts of ice can present a major hazard to flight safety. A hot-air anti-icing system uses hot air extracted from the engine compressor bleed to prevent or minimize ice buildup on protected surfaces. The fact that anti-icing devices are operated during take-off and landing when maximum power is required, makes the power loss due to air bleeding even more critical. This necessitates a better understanding of the complex aero-thermal phenomena governing the efficiency of an anti-icing piccolo tube system used to prevent ice formation on the leading edge of critical aerodynamic surface of aircraft. This is to maximize system performance and minimize the fuel consumption penalty from hot air bled from the engine. Experimental and computational studies were performed on various wing anti- icing systems that use hot air bled from the engine compressor through piccolo tube. Experiments were conducted in a bleed air laboratory of a local general aviation company to evaluate the heat transfer performance of an inner-liner and a D-duct hot air anti-ice system. With the experiments, key design and performance parameters of the anti-icing systems were identified. Surface temperature distributions were measured in the experiments and compared with results from a commercial heat transfer software package. A robust Computational Fluid Dynamics (CFD) package was required for providing the numerical simulation results, because computation of heat t ransfer coefficient is a complex task which becomes even more complex for multiple jets impinging on a curved surface of the interior of a wing leading edge. Although empirical correlations and analogies can be used to describe the heat contribution phenomena, they can easily fail under these conditions. Thus only a full conjugate Navier-Stokes analysis of internal and external flow, coupled with a suitable structural code to solve the conductive problem in the wing solid wall, can yield a plausible prediction of the heat transfer rates, and give helpful insight in the details of the phenomena. After the accuracy of this commercial package was verified with experimental data, methods for enhancing the performance of current bleed air anti-icing leading edge designs were investigated numerically. The performance of several design modifications were evaluated experimentally with a modified hot air system in the bleed air laboratory. It was concluded from this investigation that the inner-liner configuration performed better than the D-duct in term of skin temperature performance. The performance of the inner-liner configuration could be further improved by optimizing piccolo design parameters which included the total number of piccolo holes, hole pattern and piccolo hole circumferential position. In general, high system performance was associated with chocked piccolo jet flow. Finally, CFD was able to predict trends and even to some extent the magnitudes of performance of these hot air anti-icing systems.