ABSTRACT:  Viscous flow effects usually play a governing role in aerodynamic design.  Among various computational methods for viscous aerodynamic analysis, the integral boundary layer (IBL) method features distinctly rapid speed as well as other modeling conveniences.  The practical values of IBL methods are exemplified by successful software such as XFOIL for two-dimensional (2D) problems.  However, a reliable three-dimensional (3D) IBL method remains to be established.  This talk will introduce the IBL method, with a focus on the challenges and progresses in the development of 3D IBL methods.