These proceedings contain the lectures of the IUTAM Symposium dedicated to the one-hundredth anniversary of Boundary Layer research. About 40 experts of this field gave lectures on their most outstanding results in this topic. This volume is unique in that a scientific collection of articles of this calibre covering this subject will probably be the only one of its kind for the next decade. All articles have been peer reviewed. Topics covered include classification, definition and mathematics of boundary layers; instability of boundary layers and transition; boundary layers control; turbulent boundary layers; numerical treatment and boundary layer modelling; special effects in boundary layers.