A method based on a genetic algorithm (GA) is used to design the optimum configuration of defects that when put within a photonic-crystal (PhC) taper improve the coupling efficiency between dielectric and PhC waveguides (WGs). This approach optimizes the whole configuration of defects simultaneously and, therefore, takes into account the correlation among the defects. Transmission efficiencies up to 94% have been predicted for a 3-μm-wide dielectric WG into a single-line-defect PhC-WG. This result significantly improves the transmission efficiency of the same PhC taper without defects. The influence on the coupling efficiency of the PhC taper length and geometry are also discussed.