An introduction to the theory of superfluid turbulence

In this paper I first describe some aspects of the theory of counterflow turbulence. I then devote most of the paper to grid turbulence, where the theory is less well developed, although I make use of an important experimental result obtained with a more complicated type of flow generated by two counter-rotating discs. My aim is to stimulate interest in the theory of superfluid turbulence, particularly, at this stage, in the simple case of grid turbulence, among both low temperature physicists and those with a background in classical fluid mechanics. I focus on open questions and unsolved problems, questions and problems that are clearly seen in grid turbulence, but which are more widely relevant. My own background is in experimental quantum fluids. I tend to speculate about what I see as the physics of superfluid turbulence. (orig.)