The theory of integral equations has close contacts with many different areas of mathematics. Foremost among these are differential equations and operator theory. Many problems in the fields of ordinary and partial differential equations can be recast as integral equations. Suffice it to say that there is almost no area of applied mathematics and mathematical physics where integral equations do not play a role. In many ways one can view the subject of integral equations as an extension of linear algebra and a precursor of modern functional analysis.