The paper is concerned with turbulence in a superfluid, in which flow is strongly influenced by the quantum effects that give rise to two-fluid behaviour, frictionless flow of the superfluid component, and restrictions on rotational motion. There is now significant experimental evidence relating to simple forms of turbulent flow in superfluid He-4 in circumstances where comparison is possible with an analogous flow in a classical fluid. The similarities and differences are analyzed, and the evidence is assessed for quasi-classical behaviour at large length scales in the quantum case. Dissipative processes at small length scales in the superfluid are discussed; they are shown to lead to an effective viscosity but to be based on novel quantum processes. The need for further experiments, especially at very low temperatures and in superfluid He-3-B, is emphasized. (C) 2003 Elsevier Science B.V. All rights reserved.