The aim of this book is to describe the methods leading to mechanical and numerical modelling of the linear vibrations of elastic structures coupled with internal fluids (sloshing, hydroelasticity and structural acoustics). It is characteristic of the problems under consideration that they are multidisciplinary involving structural and fluid representation and related numerical aspects. The problems are solved by direct resolution of the coupled systems by finite element methods and modal reduction procedures using the eigenmodes of "elementary subsystems". The numerical methods described in this book have applications in various engineering disciplines such as the automotive and aerospace industries, civil engineering, nuclear engineering and bioengineering.