This is the Fourth Edition of the Catalog of Low-mass X-ray Binaries (LMXBs) in the Galaxy and the Magellanic Clouds. The catalog has a companion catalog of high-mass X-ray binaries (HMXBs) which is called HMXBCAT in the HEASARC database system). The catalog contains source name(s), coordinates, X-ray flux, system parameters, and stellar parameters of the components and other characteristic properties of 187 low-mass X-ray binaries, together with references to a comprehensive selection of the relevant literature. The aim of this catalog is to provide some basic information on the X-ray sources and their counterparts in other wavelength ranges (gamma-rays, UV, optical, IR, and radio). Some sources, however, are only tentatively identified as low-mass X-ray binaries on the basis of their X-ray properties being similar to the known low-mass X-ray binaries. Further identification in other wavelength bands is needed to finally determine the nature of these sources. In cases where there is some doubt about the low-mass nature of the X-ray binary, this is mentioned. Literature published before 1 October 2006 has, as far as possible, been taken into account. This online catalog was created by the HEASARC in September 2007 based on machine-readable tables obtained from the ADC/CDS data centers (their catalog J/A+A/469/807, tables lmxb.dat and lmxbnote.dat). This is a service provided by NASA HEASARC .