AbstractStrawberry breeding has been carried out since 1933 by the Department of Agriculture for Scotland with the collaboration of the West of Scotland Agricultural College, at Auchincruive, near Ayr. The objectives have been the production of varieties resistant to Red Core Root Rot (Phytophthora fragariae Hickman), with fruiting characters acceptable to commercial growers, and to develop them free from other diseases. Very high resistance is obtained but new strains of the causal organism attack previously resistant varieties. The main sources of resistance have been No. 52 (believed to be Frith) and the American variety Aberdeen. Other sources have been used more recently. Pure species have not helped but Little Scarlet, generally considered a form of Fragaria virginiana appears to increase resistance. Inheritance of resistance is estimated on the proportion of seedlings to become infected in the first year of exposure to natural inoculum in infected soils. Susceptible varieties yield families of which 100 percent are susceptible while resistant types may show less than 20 percent susceptibility under similar conditions. A few varieties were released early in the work as a temporary expedient for local use but the main introduction up to date is the variety Auchincruive Climax now of very considerable importance throughout the British Isles.