This standard addresses the capability of window units to frustrate the 'opportunity' crimes committed by unskilled and semiskilled burglars. The skilled or rarely used methods of gaining entry through window units are not addressed. This standard is compatible with the NILECJ standards for the physical security of single-swing entry doors and sliding glass door units. For the purposes of this standard, window units are classified into four security levels: minimum, moderate, medium, and relatively high. Window units are further classified by their mode of operation: sliding, outswinging, inswinging, pivoted, fixed, and security. The document provides definitions of technical terms and summarizes the window unit requirements including resistance to disassembly; resistance to loiding (a method of manipulating a locking device from the outside); locking device stability and strength; window strength; and glazing, sash frame, and security bar impact strength. A detailed description of testing procedures is given, and an appendix describes test equipment suitable for use in evaluating the physical security of window units. Two references are appended. (Author abstract modified)