This paperback edition of Dr Hudson's advanced textbook presents the theory of small disturbances propagating through solids. The material is set out carefully in mathematical detail. The linearised theory of elasticity has now been replaced by a more fundamental approach based on a generalised theory of continuum mechanics. Despite this change of emphasis in solid mechanics there remain important areas of physics in which the linear theory is clearly of fundamental importance, especially in seismology, noise analysis and the non-destructive testing of materials. This is a textbook suitable for advanced undergraduates in a variety of disciplines, including applied mathematics, applied physics, geophysics and structural and civil engineering. The book is of particular interest to seismologists and physicists engaged in non-destructive testing.