Wind is fundamentally important to cyclists since it affects their performance, bicycle control, balance and road safety. The overall aim of this research is to improve the understanding of the effect of cycling position and crosswinds on the aerodynamics and performance of a cyclist. The first part of this thesis focuses on cycling position. To minimise air resistance, cyclists lower their torso to become more aerodynamic. Results show that lowering torso angle is associated with impairment of physiological functioning, which can be explained by a combination of mechanical and muscular factors. Consequently, there is a trade-off between aerodynamic gains and physiological impairment. Therefore a mathematical model has been developed predicting the optimal torso angle at different cycling speeds. The second part of this thesis aims to understand the flow mechanics around a cyclist subjected to crosswinds. Both wind tunnel experiments and computational fluid dynamics simulations of the flow around a cyclist are used to reveal the effect of crosswinds on cyclists in different cycling positions. This thesis provides a unique approach to study cycling performance and safety by jointly investigating the human physiology and aerodynamic performance.