An experimental study has been made of the conditions in the turbulent wake behind a cylinder in an air stream at cylinder Reynolds numbers between 100 and 7000. The measurements include the mean velocity distribution, the distribution of the three components of turbulence, the statistical distribution in time of the turbulent velocity components, and the correlation derivatives in the downstream direction for both the longitudinal and transverse correlations. It is shown that the intensities of the three components of turbulent velocities are nearly equal except at the centre of the wake, where the balance between viscous decay and diffusion from the regions of shear results in a considerably greater intensity for the component at right angles to the direction of flow and also to the axis of the cylinder, i.e. in the direction of diffusion of turbulent energy. An analysis of the energy in the wake proves that complete dynamical similarity in the wake, if it is ever attained, does not occur closer to the cylinder than 1000 diameters, and that the viscous dissipation of energy can be described in terms of a length parameter, nearly constant over the width of the wake and approximately equal to the measured value of Taylor's scale of micro-turbulence.