I review the current status of the investigations of the kilohertz quasi-periodic oscillations that have been discovered in low-mass Xray binaries (LMXBs) with NASA’s Rossi X-ray Timing Explorer (RXTE) since February 1996. Seven sources have now shown this new phenomenon, one Z source (Sco X–l) and 6 atoll sources (all X-ray bursters), and some patterns are beginning to emerge. The frequencies of the oscillations are between 500 and 1200 Hz. They can be coherent for more than 102 cycles, but a more typical coherence is several 101. Amplitudes are between 0.5 and 16% (rms) of the total flux. Most sources show double kHz peaks separated by a few 102 Hz, which move up and down in frequency together. In Sco X–l the peak frequencies systematically increase, and the peak separation systematically decreases, with Ṁ. In 4U 1728–34 a third oscillation is seen at a frequency equal to the difference frequency of the two kHz peaks, but only during X-ray bursts. A simple interpretation in terms of a beat-frequency model with the difference frequency being the neutron star’s spin, as suggested by this result, is inconsistent with the fact that in Sco X–l the peak separation varies.