Internal waves are the waves in the interior of the ocean. They exist on the interface between layers of different densities. Internal waves are significant players in ocean dynamics, as they carry significant part of ocean interior kinetic energy over large distances and provide one of the links between large scale, mostly two dimensional motion and the isotropic turbulence resulting from internal wave breaking.

Despite decades of intense study of intense waves, we still are far from complete understanding of this fascinating phenomenon. There are many open questions about internal waves: how they are formed, how they propagate through the ocean, how the spectral energy of internal waves is formed and evolve, and how they break and contribute to ocean mixing, to name just a few.

Currently State of the Art Global Simulation Models currently do not resolve internal waves, nor there any hope to fully resolve them in foreseeable future. Therefore first principle understanding of internal waves is a necessary prerequisite to be successful in weather and climate modeling.

Original papers dealing with physics of internal waves are invited for this special issue of the journal of Fluid Mechanics. We will welcome papers presenting analytical, numerical and observational approaches to internal wave research. We hope to set up the stage for future internal wave research.