New empirical scaling models for frequency dependent duration of strong ground motion are presented. These were developed by regression analysis of nearly 2000 three component recordings of strong ground motion, mainly in California. The large amount of data allowed resolution of path dependence of strong motion duration, and, for the first time, of a branch of distance dependence, for epicentral distances grater than about 60 to 70 km where reflections of waves from the Moho may be recorded. A variety of scaling parameters describing the local geology and soil at the site, and the propagation path were considered, and a comprehensive analysis of their significance in affecting the duration is presented. These scaling parameters include the depth of sediments, the local geologic site condition categorical variable, s, first introduced in the late 1970's, the local soil condition categorical variable, s sub L, the average soil velocity in the top 30 m, v sub L, and related categorical variable, percentage of rock and sediments along the surface projection of the wave path, and eight types of wave paths considering number of crossings of high impedence contrast boundaries (e.g., boundaries of sediments and rocks). Finally, a variety of final models are presented, based on various combinations of the scaling parameters. The choice of model in a future application would depend on the availability of various scaling parameters for the particular problem, and on the preference of the user. These models can be used to predict frequency dependent duration of strong ground motion at a site that will not be exceeded with specified confidence, given that an earthquake has occurred at a particular location. The size of the earthquake can be specified by the earthquake magnitude. As another alternative, the strong motion duration can be estimated only from the local intensity of shaking at the site.; The duration of strong ground motion is strongly correlated with damage to structures, and opportunity for liquefaction and landslides, and it must be considered in design of earthquake resistant structures.