The inception of cavitation in a liquid medium is dependent on a variety of hydrodynamic and nonhydrodynamic effects which complicate the problem of scaling. Cavitation occurs in zones of low pressure hydrodynamically produced by flow relative to the boundaries. It is well known that changes in flow rate and size will modify the local hydrodynamic conditions, although the exact role of boundary-layer growth and associated turbulence on local pressures is not understood completely. In addition, it has been observed that cavitation inception is not always reproduced at the same hydrodynamic conditions, but seems to depend in some way on the physical properties and states of the liquid, the solid boundaries, and the entrained solid and gaseous matter. The investigation in progress at the M.I.T. Hydrodynamics Laboratory is directed at the general problem of scale effects in cavitation inception. The initial experiments have been concerned with the influence of boundary layers and turbulence on the pressure of cavitation inception and the location of inception relative to the solid boundary. The study necessarily has involved the role of gas bubbles as nuclei for cavitation and the interrelation of the stability of small gas bubbles, their size and space distribution, and the velocity and pressure variations in the turbulent boundary layer. This paper is a discussion of this combination of factors.