The present book contains contributions presented at the Third Symposium on Hybrid RANS-LES Methods, held in Gdansk, Poland, 10-12 June 2009, being a continuation of the first symposium taking place in Stockholm (Sweden, 2005) and the second in Corfu (Greece, 2007). The contributions to the Corfu symposium were published as Advances in Hybrid RANS-LES Modelling (NNFM, Vol. 97). At the Gdansk symposium, along with four invited keynotes, another 28 papers were presented addressing topics on Unsteady RANS, LES, Improved DES Methods, Hybrid RANS-LES Methods, DES vs. URANS and other Hybrid Methods, Modelling-related Numerical Issues and Industrial Applications. Additionally, a comprehensive summary of a round-table discussion on hybrid RANS-LES methods is presented. The present book reflects recent activities and new progress in the development and applications of DES and other hybrid RANS-LES modelling approaches to handle both industrial and fundamental flow problems.