This book is about the mathematics of percolation theory,with the emphasis upon presenting the shortest rigorous proofs of the main facts.I have made certain sacrifices in order to maximize the accessibility of the theory,and the major one has been to restrict myself almost entirely to the special case of bond percolation on the cubic lattice Zd.Thus there is only little discussion of such processes as continuum,mixed,inhomogeneous,long-range, first-passage,and oriented percolation.Nor have I spent much time or space on the relationship of percolation to statistical physics,infinite particle systems,disordered media,reliability theory,and so on.With the exception of the two final chapters,I have tried to stay reasonably close to core material of the sort which most graduate students in the area might aspire to know.No critical reader will agree entirely with my selection,and physicists may sometimes feel that my intuition is crooked.