The results of experiments designed to investigate the shock-induced boundary layer on a semi-infinite flat plate are described.Those for the laminar boundary layer are shown to be in agreement with a theory due to Lam & Crocco (1958) which describes two distinct domains, one near the shock where the flow is quasi-steady in a shock-fixed co-ordinate system and an unsteady region in which the flow characteristics approach the familiar steady state asymptotically. Experimental results are also presented for the non-laminar boundary layer. In particular the transition to turbulence in this unsteady boundary layer is discussed in some detail.‘Establishment times’ for steady boundary layers are given for both laminar and turbulent flows, and their relevance to the testing times available in shock tubes is discussed. The measured heat transfer rates are compared with existing theories.