The subject of turbulence remains and probably will remain as the most exciting one for the mind of researchers in a variety of ?elds. Since publication of the ?rst edition of this book in November 2001 a number of otherbooksonturbulencehaveappeared,forexampleBernardandWallace (2002), Oberlack and Busse (2002), Foias et al. (2001), Biskamp (2003), Davidson(2004),Jovanovich(2004),SagautandCambon(2008)tomention afew. Soonehastoaskagain thequestionwhyasecondeditionofonebook from a ?eld of so many on the same subject? Does it make any di?erence? Thereareadditionalreasonsapartofthosegiveninthe?rstedition. One of thebasic premises of this bookis thatWeabsolutelymustleave roomfor doubtor thereis noprogress and nolearning. Thereis nolearning without posing a question. And a question requires doubt. . . Now the freedom of doubt,whichisabsolutelyessentialforthedevelopmentofscience,wasborn from astruggle with constituted authorities. . . R. Feynmann (1964). This is closely related to the term ¿conceptual ¿: the book has now a di?erent title An informal conceptual introduction to turbulence. One of the main f- tures of the ?rst edition was indeed its conceptual orientation. The second edition is an attempt to make this feature dominant. Consequently items whicharesecondaryfromthispointofview werereducedandeven removed in favour of those added which are important conceptually. This required addressing in more detail most common misconceptions, which are con- quencesoftheprofounddi?cultiesofthesubjectandwhichtravel fromone publication to another. Consequently a one page Appendix D listing some of these misconceptions in the ?rst edition became chapter 9 titled Ana- gies,misconceptions and ill de?ned concepts.

Origins of Turbulence.- Methods of Describing and Studying Turbulent Flows.- Kinematics.- Phenomenology.- Dynamics.- Structure(s) of Turbulent Flows.- Turbulence Under Various Influences and Physical Circumstances.- Analogies, Misconceptions and Ill-Defined Concepts.- Conclusion/Close.- Appendix A. What is Turbulence?.- Appendix B. About the `SNAGS¿ of the Problem.- Appendix C. Glossary of Essential Fluid Mechanics.- Appendix D: Glossary of Some Terms.