**Table of Contents**

This part of the BETL documentation serves as an introduction to
Boundary Element Methods — in particular it is meant to be an
introduction to symmetric Galerkin-based three-dimensional Boundary
Element Methods. Naturally, this introduction is neither a comprehensive
treatise on Boundary Integral Equations nor gives it an detailed overview
on their respective discretisation schemes, the Boundary Element
Methods. For this the reader is referred to well-known literature like,
e.g., [GlEtAl03], [Hckbsch89],
[HsWdlnd08], [McLn00],
[StrSchwb11], [Stnbch08],
[StrdhrEtAl08]. This introductory chapter is
basically about the definition of a common language. Hence, even if you
are familiar with Boundary Element Methods *(and we assume that
you are!)* at least a rough reading through this chapter is
recommended since it may help to clarify the notion of expressions.