Precise radar cross section (RCS) measurements of an arbitrary target require the measurement radar system to be calibrated with a highly accurate "known" RCS target. To minimize calibration errors, RCS calibration "targets" generally meet two demanding criteria: (1) the RCS must be precisely known; (2) the calibration target must have realistic and affordable fabrication tolerances. Surprisingly, the commonly used conducting calibration sphere is generally a poor calibration object (see Kent, B.M. et al., Proc. 18th Annual Symposium, Antenna Measurement Techniques Association, p.383-8, 1996). We review recent Air Force Research Laboratory (AFRL) research which successfully produced several precision RCS calibration targets. Our measured calibration performance has been validated through a carefully controlled program of inter-range comparison measurements, whose results are presented here. AFRL's improved RCS calibration standards have reduced typical calibration errors from /spl plusmn/1.3 dB to /spl plusmn/0.25 dB for many RCS measurement systems.