The forces required to maintain a highway vehicle on the selected course at the desired speed are provided by the frictional coupling between the pavement and the tires. Under certain driving conditions the friction demand may exceed the available friction. The resultant skidding will lead to loss of control and possibly an accident. The strength of the friction coupling depends on the properties of the tires, the suspension and the pavement. On clean, dry pavements friction is adequate for all but the most severe driving maneuvers. But friction is reduced drastically when the pavement is wet, covered with snow or ice, or contaminated. An overview of the factors affecting tire-pavement friction under wet conditions is given in this paper. Also some means for improving the friction coupling are discussed. Wet pavements also reduce night visibility and produce splash and spray. Both of these effects reduce highway safety, the subject of this conference.