Studies have been made of the effect of cyclic temperature changes and wet/dry cycling on the residual stresses in marine coatings applied to steel substrates. A thermoplastic and a thermoset have been use as single coatings and as bi-layers consisting of the thermoset applied on top of the thermoplastic. Cyclic changes associated with differential thermal expansion/contraction between substrate and coating and with water absorption or desorption were observed, and it was found in addition that progressive changes in residual stress were sometimes superimposed on the cyclic changes. The effect was larger with the thermoplastic coating than with the thermoset. The stresses developed in the bi-layers were generally smaller than those in single layer coatings and were generally less sensitive to the cyclic changes in conditions. The effects were partly controlled by the thicknesses of the two layers in the bi-layer coatings. Stresses as high as 6 MPa were measured during the course of this work, a significant fraction of the failure strength of the coatings.