The aim of this book is to acquaintthe reader with the phenomenon of sup- conductivity and the high temperature superconductors discovered in 1986 by Bednorz and Muller. Just after this discovery, a lot of research work was carried out by the scientists worldwide over for more than about 10 years. This book describes the superconductivity phenomenon (Chap. 1), the structureofhighT superconductors(Chap.2),thecriticalcurrents(Chap.3), c synthesis of high T superconductors (Chap. 3), the superconductivity in c cuprates (Chap. 4), proximity e?ect and SQUID devices, their design criteria and noise aspects (Chap. 6), theories (Chap. 7) and applications (Chap. 8). TheauthorisgratefultoProfessorO.N.Srivastava,BanarasHinduUniv- sity,VaranasiforvaluableguidanceanddiscussionsduringPh.D.tenureofthe author andalsothankful to Prof.R.S. Tiwari,Dr. K.Ramakrishna,Dr. Balak Das, Dr. K.K. Verma, Dr. G.D. Varma andDr. H.K. Singh, who workedalong with the author during researchat B.H.U., leading to his Ph.D. The author is thankful to Prof. D.P. Tiwari (Head, Physics Department, A.P.S. University, Rewa), Dr. A.P. Mishra and Dr. S.L. Agrawal, Physics Department, A.P.S. University, for boosting the morale. The author is thankful to scientists and researchers whose work/papers have been consulted for preparing the manuscript. Further I wish to express thanks to Mr. Dharmendra Saxena for preparing type-script.