A mass analyzer based on a rectilinear geometry ion trap (RIT) has been built, and its performance has been characterized. Design concepts for this type of ion trap are delineated with emphasis on the effects of electrode geometry on the calculated electric field. The Mathieu stability region was mapped experimentally. The instrument can be operated using mass-selective instability scans in both the boundary and resonance ejection versions. Comparisons of performance between different versions of the device having different dimensions allowed selection of an optimized geometry with an appropriate distribution of higher-order electric fields. Comparisons made under the same conditions between the performance of a conventional cylindrical ion trap and a RIT of 4 times greater volume show an improvement of 40 times in the signal-to-noise ratio resulting from the higher ion trapping capacity of the RIT. The demonstrated capabilities of the RIT include tandem mass spectrometry, a mass resolution in excess of 1000, and a mass/charge range of 650 Th, all in a simple structure that is only 3.5 cm(3) in internal volume.