This manuscript describes some of my work at the Laboratoire Kastler Brossel on Casimir physics. I joined the group “Fluctuations Quantiques et Relativité” at the LKB in 2009 and got recruited in 2011 in the CNRS as Charg ́e de Recherche. Casimir physics study the many phenomena related to fluctuations-induced forces. Those include the van der Waals interaction between atoms or molecules as well as the Casimir interaction between macroscopic bodies. There are two main interpretations for Casimir interactions. In the so-called “field” interpretation, the vacuum field fluctuates and the bodies act merely as boundary conditions for those fluctuations. On the other hand, in the so-called “source” interpretation, fluctuations originates inside the matter forming the bodies and propagates through the vacuum field. The field interpretation was used by Casimir in his original paper [1] where he studied the interaction between perfectly reflecting plane-parallel plates. The fact that the plates were perfectly reflecting allowed to enforce hard boundary conditions on the vacuum field. The source interpretation is used to explain the van der Waals interaction where a fluctuating dipole in one atom creates a field which polarize the other atom which then acts back on the first atom.