We present the design, construction, and performance of TRISPEC ( Triple Range Imager and Spectrograph), a simultaneous optical and near-infrared imager, spectrograph, and polarimeter. This instrument splits the incoming light from a telescope into the three beams - one optical channel (0.45 - 0.90 mu m) and two infrared channels (0.90 - 1.85 and 1.85 - 2.5 mu m) - by means of two dichroic mirrors. It is capable of simultaneous three-band imaging or spectroscopy, with or without polarimetry. Low-resolution grisms (R similar to 70 - 360) cover a wide wavelength range of 0.46 - 2.5 mu m, simultaneously. The instrument employs three arrays - one 512 x 512 SITe CCD and two 256 x 256 SBRC InSb arrays - to cover the three channels. It has been commissioned in the imaging, spectroscopic, and polarimetric modes on the United Kingdom Infrared Telescope, the University of Hawaii 2.2 m telescope, and the Okayama Astrophysical Observatory 1.88 m telescope since 1999 June.